A device for combining annular transformers with a machine housing includes a bolt to fix annular transformers on a machine housing and a saucer-shaped plate assembled on the outer side of the machine housing. The saucer-shaped plate is bored with a central insert hole for the bolt to pass therethrough and has its outer annular portion formed with a first plane and its inner annular portion formed with a second plane higher than the first one. The two planes are connected by an annular conical portion contracting gradually toward its upper side to be positioned in the machine housing. The bolt is orderly inserted through the saucer-shaped plate, the machine housing and the annular transformers to fix securely the annular transformers on the machine housing. The bolt has its head completely positioned in the conical portion of the saucer-shaped plate, not protruding out of the machine housing.