To reduce the noise or vibration produced by stationary induction electric equipment, such as the transformer, etc., with a soundproof device having a simple constitution.

A plurality of reinforcing stays 7 and 7a are attached to the side wall 6 of a tank 5 housing the main body of electric equipment. Then, a sound insulating plate 10 for soundproof is fixed to the stays 7 and 7a by its corner sections only through fixing seats 8 having a prescribed thickness and a thin plate having a prescribed spring constant. The plate 10, in addition, is constituted in such a way that at least part of its outer peripheral edge is bent inward.