PURPOSE: To reduce the load applied to a driving source to move a projection lens smoothly by attaching a spring, which should be attached to a guide shaft for the purpose of bringing the projection lens into contact with a cam, to the guide shaft obliquely.

CONSTITUTION: A projection lens L is fixed to a lens base 1, and the lens base 1 is made slidable on a shaft 2 by a bearing and is supported on a base plate by a roll 10. A roll 4 is provided in the side part of the lens base 1 and is brought into contact with a cam plate 11 which has a cam face corresponding to magnifications. The lens base 1 is driven by a motor 16 to move along the shaft 2, and the lens base 1 is regulated by the shape of the cam face and is moved in the direction orthogonal to the shaft 2 simultaneously. In this constitution, a spring 6 is attached obliquely at an angle, e.g. in a range of 160°W170°, especially, 169° to the shaft 2, thereby reducing the load of the motor 16 to reduce its variance.