Plural pairs of connection plates (21) are placed circumferentially around a plurality of circularly-arranged electromagnets (2, 3, 4), in which the plural pairs are each a pair of two connection plates placed with a gap therebetween in a radial direction and are arranged in a longitudinal direction of the connection plates. Further, at a portion where one (21a) of the two connection plates forming a pair (21a, 21c) and one (21b) of the adjacent two connection plates forming another pair are connected to each other, an end portion (22a) of the one of the two connection plates forming the pair and an end portion (22b) of the one of the two connection plates forming the another pair, are configured to be bent in the radial direction so that these end portions (22a, 22b) are both apart from the other one (21a, 21b) of the two connection plates forming the pair, whereby the connection plates in the pair and the connection plates in the another pair are serially connected. Further, using an intermediate fixation plate (24) and a clamping plate (25), all of the connection plates (21) are placed at a position higher than an installation base level.
