A light emitting device-light receiving device assembly includes: a mount substrate having first and second surfaces, and including a first base as a raised portion on the first surface; a light receiving device having first and second surfaces, the first surface of the light receiving device being anchored on the first base; and a light emitting device, the light receiving device including a light passage portion allowing for passage of light emitted by the light emitting device, the light emitted by the light emitting device emerging to outside through the light passage portion, the first base, and the mount substrate, the light receiving device receiving externally incident light through the mount substrate and the first base, the light receiving device including an annular second base as a raised portion on the second surface of the light receiving device, and the light emitting device being anchored on the second base.