Plural pairs of connection plates are placed circumferentially around a plurality of circularly-arranged electromagnets, in which the plural pairs are each a pair of two connection plates placed with a gap in a radial direction and are arranged in a longitudinal direction of the connection plates. At a portion where one of the two connection plates forming a pair and one of the adjacent two connection plates forming another pair are connected, an end portion of the one of the two connection plates forming the pair and an end portion 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 are apart from the other one 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.