A drive unit comprising: a rotating electric machine including a rotating electric machine casing; a transmission including a transmission casing and integrated with the rotating electric machine; and a cooling structure configured to cool the rotating electric machine and the transmission, wherein the cooling structure includes a first cooling passage configured to cool the rotating electric machine and a second cooling passage configured to cool the transmission, and the first cooling passage and the second cooling passage are in communication with each other, and a common coolant flows through the first cooling passage and the second cooling passage, the second cooling passage is formed by a gap provided between the rotating electric machine casing and the transmission casing and extends in a C-shape in a circumferential direction of the rotating electric machine so as to surround an axis of the rotating electric machine, the drive unit further comprises: an inner seal member having an annular shape and disposed inside the second cooling passage, between the rotating electric machine and the transmission; and an outer seal member having an annular shape and disposed outside the second cooling passage, between the rotating electric machine and the transmission, the transmission casing includes a communication passage connecting the first cooling passage and the second cooling passage, an upstream end of the communication passage is connected to the first cooling passage on a radially-outward side relative to the outer seal member, and a downstream end of the communication passage is connected to the second cooling passage between the inner seal member and the outer seal member. a rotating electric machine including a rotating electric machine casing; a transmission including a transmission casing and integrated with the rotating electric machine; and a cooling structure configured to cool the rotating electric machine and the transmission, wherein the cooling structure includes a first cooling passage configured to cool the rotating electric machine and a second cooling passage configured to cool the transmission, and the first cooling passage and the second cooling passage are in communication with each other, and a common coolant flows through the first cooling passage and the second cooling passage, the second cooling passage is formed by a gap provided between the rotating electric machine casing and the transmission casing and extends in a C-shape in a circumferential direction of the rotating electric machine so as to surround an axis of the rotating electric machine, the drive unit further comprises: an inner seal member having an annular shape and disposed inside the second cooling passage, between the rotating electric machine and the transmission; and an outer seal member having an annular shape and disposed outside the second cooling passage, between the rotating electric machine and the transmission, an inner seal member having an annular shape and disposed inside the second cooling passage, between the rotating electric machine and the transmission; and an outer seal member having an annular shape and disposed outside the second cooling passage, between the rotating electric machine and the transmission, the transmission casing includes a communication passage connecting the first cooling passage and the second cooling passage, an upstream end of the communication passage is connected to the first cooling passage on a radially-outward side relative to the outer seal member, and a downstream end of the communication passage is connected to the second cooling passage between the inner seal member and the outer seal member.