An estimator includes a model unit that calculates a state quantity by using an input signal and a relational expression that expresses a target model, a correction signal measurement sensor that measures a correction signal for correcting the state quantity, a correction unit that outputs a value for correcting the state quantity based on the correction signal to the model unit, and a model changing unit that changes the model unit in accordance with an oil flow related value that relates to a change of flow of cooling oil. The correction signal measurement sensor is arranged to be in contact with a metal member that includes a coil conductive wire that constitutes the stator coil, a terminal connected to the coil conductive wire, and a power line connected between the coil conductive wire and the terminal, at a point on which no cooling oil drops.