A drive device (1, 41, 61, 71, 81, 91) which is configured to be mounted in a vehicle, comprising: - an electric motor including a first cooling channel which is configured to allow cooling water to circulate; - a power conversion unit that includes a power module and is configured to convert electric power from a power supply and to output electric power to be supplied to the electric motor; and - a supporting member fixed to the electric motor with the power conversion unit mounted on the supporting member, wherein: (i) the supporting member includes a second cooling channel including a supporting member channel inlet which is configured to allow the cooling water to flow through in and a supporting member channel outlet configured to allow the cooling water flow through out, (ii) the power module of the power conversion unit includes a third cooling channel including a power module channel inlet which is configured to allow the cooling water flow through in from the second cooling channel, and a power module channel outlet which is configured to allow the cooling water flow through out into the second cooling channel, (iii) the second cooling channel of the supporting member is composed of (a) a cooling channel connecting the supporting member channel inlet and the power module channel inlet and (b) a cooling channel connecting the power module channel outlet and the supporting member channel outlet, with all the cooling water flowing through the second cooling channel flows out of the supporting member through the power-module channel inlet, and returns to the supporting member through the power module outlet, (iv) the supporting member channel outlet is connected to the first cooling channel of the electric motor, and (v) the second cooling channel is (a) formed inside the supporting member, (b) provided with partitions arranged in a staggered manner and formed in the shape of a groove-shaped channel extending back and forth along the partitions. - an electric motor including a first cooling channel which is configured to allow cooling water to circulate; - a power conversion unit that includes a power module and is configured to convert electric power from a power supply and to output electric power to be supplied to the electric motor; and - a supporting member fixed to the electric motor with the power conversion unit mounted on the supporting member, (i) the supporting member includes a second cooling channel including a supporting member channel inlet which is configured to allow the cooling water to flow through in and a supporting member channel outlet configured to allow the cooling water flow through out, (ii) the power module of the power conversion unit includes a third cooling channel including a power module channel inlet which is configured to allow the cooling water flow through in from the second cooling channel, and a power module channel outlet which is configured to allow the cooling water flow through out into the second cooling channel, (iii) the second cooling channel of the supporting member is composed of (a) a cooling channel connecting the supporting member channel inlet and the power module channel inlet and (b) a cooling channel connecting the power module channel outlet and the supporting member channel outlet, with all the cooling water flowing through the second cooling channel flows out of the supporting member through the power-module channel inlet, and returns to the supporting member through the power module outlet, (iv) the supporting member channel outlet is connected to the first cooling channel of the electric motor, and (v) the second cooling channel is (a) formed inside the supporting member, (b) provided with partitions arranged in a staggered manner and formed in the shape of a groove-shaped channel extending back and forth along the partitions. (a) formed inside the supporting member, (b) provided with partitions arranged in a staggered manner and formed in the shape of a groove-shaped channel extending back and forth along the partitions.