An optical scanning device includes a light source, a scanning member, and an incident optical system. The scanning member two-dimensionally scans a scanning area with the deflected light beam in a first direction and a second direction perpendicular to the first direction. The incident optical system guides the emitted light beam to the scanning member, the incident optical system including the light source. The scanning area includes a first area and a second area surrounding the first area. When the scanning area is viewed from a side of the scanning member, at least a part of the incident optical system is disposed in an area of the second area that overlaps one of two divided areas of the scanning area. The two divided areas are divided by a line segment parallel to the first direction,

A lens array unit includes a lens array including a plurality of lenses, a first side plate, and a second side plate, the first side plate and the second side plate being configured to hold the plurality of lenses therebetween, and a frame made of resin and including a first supporting portion and a second supporting portion, the first supporting portion being in contact with an outside surface of the first side plate, the second supporting portion being in contact with an outside surface of the second side plate, the first supporting portion and the second supporting portion being configured to hold the lens array therebetween and support the lens array. The outside surface of the first side plate includes a plurality of first concave portions spaced from each other in an array direction of the lenses and configured to fit with the first supporting portion.

A lens unit includes a tube lens; a single lens arranged at a downstream side with respect to the tube lens in an optical incidence direction; and a supporting member that supports the tube lens and the single lens. Reflection light from a document is condensed on an image sensor by the tube lens and the single lens to form an image. An end surface part, not facing the tube lens, of the single lens is in direct contact with the supporting member.

A lens array unit includes a lens array including a plurality of lenses, a first side plate, and a second side plate, the first side plate and the second side plate being configured to hold the plurality of lenses therebetween, and a frame made of resin and including a first supporting portion and a second supporting portion, the first supporting portion being in contact with an outside surface of the first side plate, the second supporting portion being in contact with an outside surface of the second side plate, the first supporting portion and the second supporting portion being configured to hold the lens array therebetween and support the lens array. The outside surface of the first side plate includes a plurality of first concave portions spaced from each other in an array direction of the lenses and configured to fit with the first supporting portion.

An optical scanning device includes a light source, a scanning member, and an incident optical system. The scanning member two-dimensionally scans a scanning area with the deflected light beam in a first direction and a second direction perpendicular to the first direction. The incident optical system guides the emitted light beam to the scanning member, the incident optical system including the light source. The scanning area includes a first area and a second area surrounding the first area. When the scanning area is viewed from a side of the scanning member, at least a part of the incident optical system is disposed in an area of the second area that overlaps one of two divided areas of the scanning area. The two divided areas are divided by a line segment parallel to the first direction.

An image reading apparatus includes a light source that emits light in a main scanning direction to a subject to be read, a light receiving unit that receives light reflected by the subject to be read, and an optical system that images the light reflected by the subject to be read and guides the light to the light receiving unit. The optical system includes a reflector mirror that reflects the light reflected by the subject to be read, and an optical element that is disposed adjacent to the reflector mirror and images the light reflected by the subject to be read. The optical element is held by the reflector mirror.

An scanning lens to scan a document image includes a lens and a retainer to retain the lens bonded and fixed to the retainer by an adhesive. Conditional formula (1), or both conditional formula (2) and conditional formula (3) below are satisfied: $\begin{array}{cc}\mathrm{Vb}=0,& \left(1\right)\\ 0|{}_{\mathrm{large}}/{}_{\mathrm{small}}\left(\underset{i}{\overset{n}{.Math.}}{\mathrm{Vp}}_i-\underset{i}{\overset{n}{.Math.}}{\mathrm{Vm}}_i\right)/(\underset{i}{\overset{n}{.Math.}}{\mathrm{Vp}}_i+\underset{i}{\overset{n}{.Math.}}\end{array}$

An image sensor includes: a lens configured to focus light irradiated toward an object to be read and reflected by the object to be read; a sensor configured to receive light focused by the lens; a sensor board configured to mount thereon the sensor; a board retaining plate, having a casing attachment surface extending in the X direction and a sensor board attachment reference surface that is in contact with the +Y side of the sensor board and is formed in a side surface of the casing attachment surface, and configured to retain the sensor board; and a first casing configured to fix or retain the board retaining plate by fastening of a surface of the casing attachment surface.

An image reading apparatus includes a light source that emits light in a main scanning direction to a subject to be read, a light receiving unit that receives light reflected by the subject to be read, and an optical system that images the light reflected by the subject to be read and guides the light to the light receiving unit. The optical system includes a reflector mirror that reflects the light reflected by the subject to be read, and an optical element that is disposed adjacent to the reflector mirror and images the light reflected by the subject to be read. The optical element is held by the reflector mirror.

An scanning lens to scan a document image includes a lens and a retainer to retain the lens bonded and fixed to the retainer by an adhesive. Conditional formula (1), or both conditional formula (2) and conditional formula (3) below are satisfied:

[00001]$\begin{array}{cc}.Math.\mathrm{Vb}=0,& \left(1\right)\\ 0\left|{}_{\mathrm{large}}.Math.\text{/}.Math.{}_{\mathrm{small}}\left(\underset{i}{\overset{n}{.Math.}}.Math.{\mathrm{Vp}}_i-\underset{i}{\overset{n}{.Math.}}.Math.{\mathrm{Vm}}_i\right).Math.\text{/}.Math.\left\{\underset{i}{\overset{n}{.Math.}}.Math.{\mathrm{Vp}}_i+\underset{i}{\overset{n}{.Math.}}.Math.{\mathrm{Vm}}_i\right)\right|<3.5.Math..Math.\left(i=1,2,\mathrm{.Math.}.Math..Math.n\right),.Math..Math.\mathrm{and}& \left(2\right)\\ .Math.0<\mathrm{Vb}.Math.\text{/}.Math.\mathrm{Va}<0.5.& \left(3\right)\end{array}$