A moisture sensor detects moisture in an object. A first light-emitting element emits light. A first reflecting member reflects light reflected from the object toward the object. A light-receiving element receives light that is multiple reflected between the object and the first reflecting member. A controller determines an amount of moisture in the object based on a light reception result from the light-receiving element.

A plurality of light receiving lenses are arranged along a main scanning direction. A plurality of light receiving elements are arranged in a line along the main scanning direction, and receive light transmitted through the plurality of light receiving lenses. The plurality of light receiving elements form at least two rows of reading lines. The light receiving lenses constitute a telecentric optical system, and a width W1 in a sub-scanning direction is smaller than a width W2 in the main scanning direction.

An optical sensor includes a light emitting unit configured to emit and output light, a light receiving unit configured to receive light, a substrate on which the light emitting unit and the light receiving unit are mounted, an electrically conductive pattern including a land to be electrically connected to an electrode of the light emitting unit, a resist arranged as a layer above the electrically conductive pattern or the substrate, a light shielding layer provided as a layer above the resist, and a light shielding region formed by a portion of the land and a portion of the light shielding layer overlapping in the direction of the normal of a mounting surface of the substrate, to shield stray light directed towards the substrate from the light emitting unit.