Provided is a temperature derivation method for deriving an oil film temperature of a lubricant in a device, the temperature derivation method including a measurement step of measuring a dielectric constant of the lubricant by applying an alternating voltage while changing a frequency to an electric circuit configured by the device, a derivation step of applying the dielectric constant measured in the measurement step to a theoretical formula to derive a relaxation time of the lubricant, and a calculation step of calculating the oil film temperature by using the relaxation time.