An image reading device includes a board including a plurality of imaging elements arranged along a scanning direction, and a housing including a plurality of optical components that are arranged along the scanning direction and a plurality of housing components that are arranged along the scanning direction. Each of the plurality of optical components focuses light reflected by a reading target onto a corresponding imaging element, and each of the plurality of housing components holds at least one optical component. The plurality of housing components are arranged to have a clearance therebetween and each of the plurality of housing components is fixed to the board at a position to transmit light through the optical components to focus onto the corresponding imaging element.

An optical line sensor reads an inspection object conveyed in a sub-scanning direction by a reading line L extending in a main scanning direction and includes a plurality of light-receiving lenses 11 and a plurality of light-receiving elements. The plurality of light-receiving lenses 11 are arranged along the main scanning direction. The plurality of light-receiving elements are arranged linearly along the main scanning direction, and receive light transmitted through the plurality of light-receiving lenses 11. The plurality of light-receiving lenses 11 are arranged to be separated from each other by a diameter of the light-receiving lens 11 or longer. A plurality of light-receiving elements 121 form at least one row or more of the reading lines L.