A communication module according to the present invention includes a substrate, a laser element and a light receiving element provided on a front surface of the substrate and separating from each other, a transparent resin package collectively sealing the laser element and the light receiving element, and a diffusion unit provided to be opposed to a light emitting surface of the laser element at a prescribed distance for diffusing a laser beam emitted by the laser element, while the distance T between the laser element and the light receiving element satisfies the following formula (1): T≧t1·tan θ+(t1+t2)·tan θ′ . . . (1) (in the formula (1), t1 represents the distance between the light emitting surface of the laser element and the diffusion unit, θ represents the maximum angle of emission of the laser element, t2 represents the difference between the height from the front surface of the substrate up to the light emitting surface and the height up to alight receiving surface of the light receiving element, and θ′ represents the maximum diffusion angle of the diffusion unit.)