a first heat radiation unit is formed on one surface of the imaging unit in a vertical direction . a second heat radiation unit is formed on the other surface of the imaging unit in the vertical direction . a third heat radiation unit is formed on a surface opposite to an imaging direction of the imaging unit . a first heat transfer unit transfers heat of a first heat source of the imaging unit to the first heat radiation unit and the third heat radiation unit . a second heat transfer unit transfers heat of a second heat source of the imaging unit , which has a higher maximum allowable temperature than the first heating unit , to the second heat radiation unit . a heat insulation unit suppresses heat transfer between the first and the second heat radiation units and between the third and the second heat radiation units .