A camera-mounting device is provided that is inexpensive and resistive to vibration, and can generate a large coupling force with a small operation force. The camera-mounting device includes a ball shaft, a case main body provided with a ball-shaft receiver, a press plate that allows the ball shaft to be pressed onto the ball-shaft receiver and a cam that presses the press plate in a direction toward the ball shaft by a rotation of a lever, and in this structure, the rotation of the lever is made to have a multiplied force through the principle of the lever to push the press plate down so that the cam and a cam contact face are made in contact with each other on a flat face. With this arrangement, a large coupling force is generated by a small force so that the device is made resistive to vibration.