The optical scanner comprises: a rotor being attached to one end part of a rotor shaft; a polygon mirror having reflective surfaces and being attached to the rotor shaft; and a bearing section being provided to a stator housing and capable of rotatably holding the rotor shaft. A recessed part, through which the rotor shaft is penetrated, is formed in a top part of the polygon mirror. A retainer section of the rotor shaft, which is provided in the recessed part, and an elastic member, which is provided between the retainer section and an inner bottom part of the recessed part and which always biases the polygon mirror toward the rotor, are accommodated in the recessed part together with an end part of the rotor shaft.