A light scanning device has a light deflecting member such as a polygon mirror rotated to thereby scan with a light, a bearing member for rotatably supporting the light deflecting member, a supporting member for holding the bearing member, and a base member formed integrally as a one-piece construction with the supporting member. The light deflecting member is accurately held relative to the base member by the highly accurately provided supporting member. The light scanning device is characterized by the integral molding for improving the accuracy of an optical system member which has heretofore been made discretely and thereafter coupled to the base member, and is preferably characterized by the integral molding of a supporting portion (a positioning and containing portion) for supporting a plurality of optical system members relative to the base member.