In the transmitter receiver of the present invention, a light-shielding sheet is arranged in front of a light-emitting portion having a LED whose light-emitting central axis is inclined and an aperture from which only the head of the light-emitting portion is exposed is made in the light-shielding sheet. The light-shielding sheet masks the inclined side portion of the light-emitting portion to prevent a light-receiving portion from detecting the light leaking from the inclined side portion. Therefore, the light-receiving portion can detect with high accuracy a change in the amount of light emission that is produced by a change in the direction of the light-emitting portion.