A thermometer includes a first surface temperature measurement unit; a first reference temperature measurement unit; a second surface temperature measurement unit; a second reference temperature measurement unit; a temperature correction unit that calculates a mounting positional difference between the first and second surface temperature measurement units from a measurement subject and a mounting positional difference between the first and second reference temperature measurement units from the measurement subject in terms of temperature differences that compensate for temperature dependence, thus correcting the first surface temperature and first reference temperature, or the second surface temperature and second reference temperature; and a core temperature calculation unit that calculates a core temperature of the measurement subject using the first surface temperature and first reference temperature or the second surface temperature and second reference temperature corrected by the temperature correction unit.