Cooling structure for photoelectric conversion element

A cooling mechanism for a surface-mounted-type photoelectric conversion element which has a signal terminal and a terminal for fixation at a back surface thereof, wherein the signal terminal is connected to internal wiring and the terminal for fixation is not connected to the internal wiring, the cooling mechanism comprising:

• a front-surface-side copper foil pattern which is provided on a front surface of a circuit board and to which the terminal for fixation is connected, the front surface being located at one side in the thickness direction of the circuit board;
• a back-surface-side copper foil pattern which is provided on a back surface of the circuit board, the back surface being located at the other side in the thickness direction of the circuit board;
• a through-hole via which connects the front-surface-side copper foil pattern and the back-surface-side copper foil pattern;
• and
• a cooling member which is fixed to the circuit board so as to have contact with the back-surface-side copper foil pattern, and which cools the back-surface-side copper foil pattern.