In a power converting transformer, an I-core has a pair of fixing grooves provided at centers on opposite side surfaces of the I-core in a y-direction in an xyz orthogonal coordinate system, the fixing grooves extending through the I-core in the z-direction, and an E-core has a pair of fixing recess portions provided at x-direction centers of the y-direction opposite end portions of the base portion on a surface opposite from a surface of the base portion facing the I-core. The I-core and the E-core are pressed and fixed to each other by a fixing spring wrapped around the I-core and the E-core through the fixing grooves and the fixing recess portions. An x-direction length of the E-core is shorter than an x-direction length of the I-core, and a y-direction length of the E-core is shorter than or equal to a y-direction distance between the fixing grooves of the I-core.