A device for assessing remaining life of a rotating electrical machine includes: a data acquisition unit configured to acquire actual running performance data and electrical data about the rotating electrical machine to be assessed; an index value calculation unit configured to calculate a first index value to a third index value based on the acquired data, and to calculate, as a fourth index value, an estimation value of a residual withstand voltage value of the rotating electrical machine by performing analysis that uses an MT method on each piece of the electrical data; and an insulation deterioration estimation unit configured to assess the remaining life of the rotating electrical machine by estimating the remaining life of the rotating electrical machine with use of four index values from the first index value to the fourth index value.