To directly cool a ventilation fan motor part by the outside air while suppressing noise.

In a co-generation device enclosed by a soundproof case 1, in an upper side to an exhaust port 53 of the soundproof case 1, a ventilation fan 45 is provided, by forming a roof plate 27 of the soundproof case 1 in a double structure of an upper/lower side ceiling plate 31, 32, a cavity part 33 is formed, an outside air suction passage communicating outside the soundproof case 1 and the cavity part 33 is provided, a motor opening 51 is provided in the lower side ceiling plate 32 in a side of the exhaust port 53, a motor part 45a of the ventilation fan 45 is made to face in this motor opening 51. In the soundproof case 1 generating a negative pressure by driving the ventilation fan 45, by sucking the outside air through the outside air suction passage, cavity part 33, and the motor opening 51, in-the ceiling cooling air 52 cooling the motor part 45a of the ventilation fan 45 is generated, the motor part 45a of the ventilation fan 45 is directly cooled by the outside air not heated.