This invention is provided with: a wind tunnel (9) that, while keeping an insulating distance to pair-forming coils (2), surrounds a region from a yoke portion (3b) of a core (3) to at least a part of the pair-forming coils (2), to thereby guide a flow of cooling air for the pair-forming coils (2) into an extending direction of leg portions (3c); a supporting structural member (4) that is fixed to the yoke portion (3b) to support inside the wind tunnel (9), the core (3) and the pair-forming coils (2); and a windshield plate (8) that partly shields a gap between the pair-forming coils (2) and the wind tunnel (9); wherein, in the supporting structural member (4), air holes (4h) for passing the cooling air therethrough are formed in corresponding to inner gaps (Fc2, Fc3) of the coils (2).