A relay control method of an in-vehicle motor comprising a motor control module that controls the in-vehicle motor and has, inside a housing, a power supply relay connected to a battery, and a motor drive circuit connected to a fixed contact of the power supply relay via a bus bar, wherein: the motor drive circuit is arranged in contact with a heat radiation part that has a higher thermal conductivity than the power supply relay; characterized in that: the motor control module further comprises a phase relay connected to the motor drive circuit via a bus bar; wherein when an ignition ON operation is not carried out after the ignition OFF operation, determining if an ambient temperature condition is satisfied in which an ambient temperature is equal to or less than a predetermined temperature; maintaining a switch of the power supply relay and a switch of the phase relay in the on state for a first predetermined time; performing, until the first predetermined time has elapsed, a motor energization control for maintaining a rotation stop state of the in-vehicle motor by imparting a current, whereby the current value for outputting a motor torque in a motor stopped state does not change; and when the first predetermined time elapses from the start of the motor energization control, switching the switch of the power supply relay from on to off and keeping the switch of the phase relay in the on state. the motor drive circuit is arranged in contact with a heat radiation part that has a higher thermal conductivity than the power supply relay; characterized in that: the motor control module further comprises a phase relay connected to the motor drive circuit via a bus bar; wherein when an ignition ON operation is not carried out after the ignition OFF operation, determining if an ambient temperature condition is satisfied in which an ambient temperature is equal to or less than a predetermined temperature; maintaining a switch of the power supply relay and a switch of the phase relay in the on state for a first predetermined time; performing, until the first predetermined time has elapsed, a motor energization control for maintaining a rotation stop state of the in-vehicle motor by imparting a current, whereby the current value for outputting a motor torque in a motor stopped state does not change; and when the first predetermined time elapses from the start of the motor energization control, switching the switch of the power supply relay from on to off and keeping the switch of the phase relay in the on state. the motor control module further comprises a phase relay connected to the motor drive circuit via a bus bar; wherein when an ignition ON operation is not carried out after the ignition OFF operation, determining if an ambient temperature condition is satisfied in which an ambient temperature is equal to or less than a predetermined temperature; maintaining a switch of the power supply relay and a switch of the phase relay in the on state for a first predetermined time; performing, until the first predetermined time has elapsed, a motor energization control for maintaining a rotation stop state of the in-vehicle motor by imparting a current, whereby the current value for outputting a motor torque in a motor stopped state does not change; and when the first predetermined time elapses from the start of the motor energization control, switching the switch of the power supply relay from on to off and keeping the switch of the phase relay in the on state.