To provide a state detection device having a simple constitution capable of preventing return light from entering directly a light receiving element without using a special optical element such as an optical separation element or an optical isolator, and detecting surely the intensity of output light from a laser element, concerning a state detection device utilizing a self-coupling effect of a semiconductor laser element.

A condensing lens for condensing the output light from the laser element and irradiating the light toward a detection object, and reflecting a part of the output light sideward is provided so that the lens surface is tilted with respect to an output light emission surface of the laser element, and a light receiving element for receiving the output light reflected by the condensing lens is provided on a position avoiding an optical path of a return light reflected by the detection object and entering the laser element through the condensing lens.