A method for manufacturing a vehicle power transmission device (100;101;102) including a case (1;6;8;15) and a ring gear (2;7;9) fitted on an outer peripheral surface of the case to transmit drive power from a drive source, the method includes: a welding step in which an annular flange (11;61;91:23) is formed to either one of the case (1;6;8;15) and the ring gear (2;7;9), and along an abutting portion between one side surface of the annular flange and the case or the ring gear, butt-welding is performed such that ends of a weld bead are lapped; wherein the welding step includes performing laser beam welding characterized in that the method further comprises: a measurement step of measuring an outline of the other side surface of the annular flange placed in close proximity to the one side surface; and an evaluation step of evaluating a weld condition based on part of the outline, which is measured in the measurement step, of a portion corresponding to a lapping portion of the weld bead, and the evaluation step includes determining that no cracks have occurred in the weld bead if the outline measured in the measurement step is dented toward the weld bead in the portion corresponding to the lapping portion as compared to a non-lapping portion. a welding step in which an annular flange (11;61;91:23) is formed to either one of the case (1;6;8;15) and the ring gear (2;7;9), and along an abutting portion between one side surface of the annular flange and the case or the ring gear, butt-welding is performed such that ends of a weld bead are lapped; wherein the welding step includes performing laser beam welding characterized in that the method further comprises: a measurement step of measuring an outline of the other side surface of the annular flange placed in close proximity to the one side surface; and an evaluation step of evaluating a weld condition based on part of the outline, which is measured in the measurement step, of a portion corresponding to a lapping portion of the weld bead, and the evaluation step includes determining that no cracks have occurred in the weld bead if the outline measured in the measurement step is dented toward the weld bead in the portion corresponding to the lapping portion as compared to a non-lapping portion. a measurement step of measuring an outline of the other side surface of the annular flange placed in close proximity to the one side surface; and an evaluation step of evaluating a weld condition based on part of the outline, which is measured in the measurement step, of a portion corresponding to a lapping portion of the weld bead, and the evaluation step includes determining that no cracks have occurred in the weld bead if the outline measured in the measurement step is dented toward the weld bead in the portion corresponding to the lapping portion as compared to a non-lapping portion. an evaluation step of evaluating a weld condition based on part of the outline, which is measured in the measurement step, of a portion corresponding to a lapping portion of the weld bead, and the evaluation step includes determining that no cracks have occurred in the weld bead if the outline measured in the measurement step is dented toward the weld bead in the portion corresponding to the lapping portion as compared to a non-lapping portion.