An electric motor cooling method for cooling an electric motor by using a first refrigerant, comprising: cooling the first refrigerant; and supplying the first refrigerant to the electric motor, characterized in that: the first refrigerant is oil used for lubrication and cooling of the electric motor; the first refrigerant is cooled by heat exchange with a second refrigerant having a cooling target that is different from the first refrigerant, and supplied to the electric motor after being cooled by the heat exchange; and the method further comprises reducing (S102, S105) a flow rate of the supply of the first refrigerant to the electric motor when a temperature of the first refrigerant is less than a first prescribed temperature, the reduced flow rate being less than the flow rate when the temperature of the first refrigerant is greater than or equal to the first prescribed temperature, the first prescribed temperature being a temperature indicating a state in which appropriate cooling of the electric motor by using the first refrigerant is expected; and continuously reducing (S103, S105) the flow rate of the supply of the first refrigerant as long as a temperature of the second refrigerant is less than a second prescribed temperature even after the temperature of the first refrigerant reaches the first prescribed temperature, the second prescribed temperature being a temperature indicating a state in which the second refrigerant is no longer in an excessive low-temperature state and excessive cooling of the first refrigerant by using the second refrigerant can be avoided. cooling the first refrigerant; and supplying the first refrigerant to the electric motor, characterized in that: the first refrigerant is oil used for lubrication and cooling of the electric motor; the first refrigerant is cooled by heat exchange with a second refrigerant having a cooling target that is different from the first refrigerant, and supplied to the electric motor after being cooled by the heat exchange; and the method further comprises reducing (S102, S105) a flow rate of the supply of the first refrigerant to the electric motor when a temperature of the first refrigerant is less than a first prescribed temperature, the reduced flow rate being less than the flow rate when the temperature of the first refrigerant is greater than or equal to the first prescribed temperature, the first prescribed temperature being a temperature indicating a state in which appropriate cooling of the electric motor by using the first refrigerant is expected; and continuously reducing (S103, S105) the flow rate of the supply of the first refrigerant as long as a temperature of the second refrigerant is less than a second prescribed temperature even after the temperature of the first refrigerant reaches the first prescribed temperature, the second prescribed temperature being a temperature indicating a state in which the second refrigerant is no longer in an excessive low-temperature state and excessive cooling of the first refrigerant by using the second refrigerant can be avoided. the first refrigerant is oil used for lubrication and cooling of the electric motor; the first refrigerant is cooled by heat exchange with a second refrigerant having a cooling target that is different from the first refrigerant, and supplied to the electric motor after being cooled by the heat exchange; and the method further comprises reducing (S102, S105) a flow rate of the supply of the first refrigerant to the electric motor when a temperature of the first refrigerant is less than a first prescribed temperature, the reduced flow rate being less than the flow rate when the temperature of the first refrigerant is greater than or equal to the first prescribed temperature, the first prescribed temperature being a temperature indicating a state in which appropriate cooling of the electric motor by using the first refrigerant is expected; and continuously reducing (S103, S105) the flow rate of the supply of the first refrigerant as long as a temperature of the second refrigerant is less than a second prescribed temperature even after the temperature of the first refrigerant reaches the first prescribed temperature, the second prescribed temperature being a temperature indicating a state in which the second refrigerant is no longer in an excessive low-temperature state and excessive cooling of the first refrigerant by using the second refrigerant can be avoided.