To provide an axle mounting device to eliminate the weak point of a weld part and be high in reliability on a strength.

This axle mounting device comprises a leaf spring 3 having one end pivotally mounted on a main hanger 2 fixed at the frame 1 of a car body; an axle 7 making contact with the under side of the leaf spring 3 through an upper axle seat 6; an lower axle seat 13 making contact with the lower side of the axle 7: a pair of side plates 14 fixed on both sides of the axle 7 and having upper and lower ends fixed at upper and lower part axle seats 6 and 13; and a fixing means 11 fixing the upper axle seat 6, the lower axle seat 13, and the side plate 14 at the side plate 14 at the leaf spring 3.