A light source emits light having a thin shape in a cross section viewed in the beam direction of the light. A light receiver includes a plurality of avalanche photodiodes each having a light receiving face that receives reflected light. The light receiving faces are disposed in an array at a predetermined interval along a longitudinal direction of the thin shape and the light receiver has a surface including the light receiving faces. An optical system guides the reflected light to the light receiver so that a focus point for a direction in which the light receiving faces are arrayed is set before the surface and a focus point for a perpendicular direction is set on the surface, the perpendicular direction being perpendicular to both the direction in which the light receiving faces are arrayed and the beam direction of the reflected light.