The light diffusion member includes a light diffusing body and a light diffusing layer. The optical catheter connector mates to the motor unit for coupling optical signal into and out of a catheter optical fiber and providing drive torque to the catheter optical fiber. In a first stage, the clamping device is closed to bring the sheets in complete contact with each other, by causing the above-mentioned elastic deformation of one of the sheets, in a second stage, the clamping device is opened again by a limited extent, until a predetermined position is reached, so as to define a gap between the sheets having substantially predetermined dimensions. When the operation lever is inadvertently positioned midway between the open position and a closed position, the spring member provides a restoring force to the cam pole.