The present invention achieves oil amount reduction and size reduction in a seal oil supply device for rotating electric machine by suppressing expansion of a rotary shaft due to its temperature increase and reducing the gap between the rotary shaft and a seal ring in normal operation. In this seal oil supply device for rotating electric machine, seal oil is supplied from a seal oil pump to a seal ring of a rotating electric machine in which hydrogen gas is sealed, via a differential pressure regulation valve for regulating a pressure of the seal oil. A first route is provided for supplying the seal oil from the seal oil pump via the differential pressure regulation valve, and in addition, a second route is provided for supplying the seal oil from the seal oil pump via a relief valve.