A camera employing an automatic focusing unit for detecting an optical image through a photographic lens and for outputting an image signal. The automatic focusing unit has a window for introducing the optical image thereinto and comprises a mounting member on which the automatic focusing unit is mounted. The mounting member has a hole for allowing the optical image to pass therethrough and a pair of nested mounting cylindrical members acting as a guide are provided between the mounting member and the automatic focusing unit and surrounding the optical path therebetween for guiding the automatic focusing unit in the direction toward and away from the mounting member. A biasing member, such as coil spring is provided on the outer periphery of the cylindrical members for biasing the automatic focusing unit in the direction away from the mounting member. Fixing elements are provided for adjustably fixing the position of the automatic focusing unit to the mounting member against biasing force of the coil spring so that the image receiving plane of the automatic focusing unit is placed at an optically equivalent position to that of a film plane with respect to the photographic lnes.