Provided is a contact type internal thermometer including: a measurement surface that is brought into contact with a measurement object; a first temperature sensor stack including a first measurement surface side temperature sensor and a first back surface side temperature sensor arranged on opposite sides of a first thermal resistor; a second temperature sensor stack including a second measurement surface side temperature sensor and a second back surface side temperature sensor arranged on opposite sides of a second thermal resistor; and a controller configured to calculate an internal temperature of the measurement object based on measurement results of the respective temperature sensors, in which the controller has a first mode of calculating the internal temperature based on a heat conduction equation in a non-steady state, and a second mode of calculating the internal temperature based on a heat conduction equation in a steady state.