Device for cooling and lubricating an electric power train of an electric or hybrid motor vehicle, comprising an electric machine with a wound rotor and a speed reducer which is coupled to said machine, said device comprising: a cooling circuit of said electric machine which is supplied with oil, comprising a heat exchanger which is connected, on the one hand, to a pipe for removing cooling liquid coming from a cooling liquid circuit which connects members of the electric power train passing via a radiator of the vehicle and, on the other hand, to a pipe for removing oil coming from an oil reservoir which is arranged in the lower portion of said electric machine and control means in order to supply at the output of said heat exchanger a flow of oil which is controlled in terms of temperature to an oil distribution circuit of said cooling circuit which is capable of projecting the oil which is controlled in terms of temperature and which is from said heat exchanger onto heating elements of said electric machine, whilst the oil projected in this manner is recovered in said oil reservoir, said device also comprising: a lubrication circuit of said speed reducer comprising a housing inside which the speed reducer is arranged, the base of the housing being shaped to constitute an oil store which enables the speed reducer to be lubricated by moving a volume of oil generated by the rotation of the elements of the speed reducer in contact with the oil store, said device further comprising at the output of said heat exchanger a diversion pipe which is capable of conveying a portion of the oil which is controlled in terms of temperature and which is from said heat exchanger to the inlet of a network of heat exchange pipes which are arranged in contact with the base of said housing of the speed reducer in order to enable the oil of said oil store to be cooled, the output of said network of heat exchange pipes being connected to the oil reservoir. a cooling circuit of said electric machine which is supplied with oil, comprising a heat exchanger which is connected, on the one hand, to a pipe for removing cooling liquid coming from a cooling liquid circuit which connects members of the electric power train passing via a radiator of the vehicle and, on the other hand, to a pipe for removing oil coming from an oil reservoir which is arranged in the lower portion of said electric machine and control means in order to supply at the output of said heat exchanger a flow of oil which is controlled in terms of temperature to an oil distribution circuit of said cooling circuit which is capable of projecting the oil which is controlled in terms of temperature and which is from said heat exchanger onto heating elements of said electric machine, whilst the oil projected in this manner is recovered in said oil reservoir, said device also comprising: a lubrication circuit of said speed reducer comprising a housing inside which the speed reducer is arranged, the base of the housing being shaped to constitute an oil store which enables the speed reducer to be lubricated by moving a volume of oil generated by the rotation of the elements of the speed reducer in contact with the oil store, said device further comprising at the output of said heat exchanger a diversion pipe which is capable of conveying a portion of the oil which is controlled in terms of temperature and which is from said heat exchanger to the inlet of a network of heat exchange pipes which are arranged in contact with the base of said housing of the speed reducer in order to enable the oil of said oil store to be cooled, the output of said network of heat exchange pipes being connected to the oil reservoir. a lubrication circuit of said speed reducer comprising a housing inside which the speed reducer is arranged, the base of the housing being shaped to constitute an oil store which enables the speed reducer to be lubricated by moving a volume of oil generated by the rotation of the elements of the speed reducer in contact with the oil store, said device further comprising at the output of said heat exchanger a diversion pipe which is capable of conveying a portion of the oil which is controlled in terms of temperature and which is from said heat exchanger to the inlet of a network of heat exchange pipes which are arranged in contact with the base of said housing of the speed reducer in order to enable the oil of said oil store to be cooled, the output of said network of heat exchange pipes being connected to the oil reservoir.