When the adjusting shaft is rotated, the rotation of the adjusting shaft is transmitted to the rotationally movable barrel. The rotationally movable barrel rotates so that the rotationally movable barrel moves forward and backward along optical axis while rotating due to the interaction between the female screw portion formed in the distal end of the rotationally movable barrel and the male screw portion formed in the second flange portion of the fixed barrel. The forward and backward movement of the rotationally movable barrel along optical axis causes the rectilinearly movable barrel connected to the connecting portion of the rotationally movable barrel through the groove, to move forward and backward along optical axis. Accordingly, the CCD fixed to the rectilinearly movable barrel through the CCD carrier moves forward and backward along optical axis, thereby correcting the flange-back length.