To prevent penetration of rainwater into a bonnet and to reduce leakage of noise from the inside of the bonnet.

A case body 15 open to the front having an output terminal board 17 on an upper inner wall is mounted inside two upper and lower opening parts 13, 14 formed in a bonnet 12. A packing 19 is stuck onto the periphery facing the upper opening part 13 of the case body 15, while a door 16 blocking off the upper opening part 13 is provided with an edge part 21 abutting on the packing 19.