A detecting device of the present disclosure includes a light emitting portion that emits light and a light receiving portion including an angle limiting member that limits an angle of incidence of light from the light emitting portion, wherein the light receiving portion has a first light receiving region and a second light receiving region that is spaced further from the light emitting portion than the first light receiving region is, the angle limiting member includes a first limiting region corresponding to the first light receiving region and a second limiting region corresponding to the second light receiving region, and the degree of angle limitation of the second limiting region is smaller than the degree of angle limitation of the first limiting region.