A control device (200) controls a surgical instrument (100) including a heater (160) includes a first power supply (232), a second power supply (234), a resistance value calculation section (250), and an output control circuit (220). The first power supply (232) outputs a first current having a first frequency and supplied to the heater. The second power supply (234) outputs a second current combined with the first current, supplied to the heater and having a second frequency different from the first frequency. The resistance value calculation section (250) separates a signal component related to the second current from the first and second currents having passed through the heater, and calculates a heater resistance value based on the signal component. The output control circuit (220) controls a temperature of the heater (160) based on the heater resistance value.
