Provided is a program update system for an air conditioner, which can complete update of a program without delay. A controller 51 determines whether it is summer or winter. If it is summer or winter, the controller 51 updates a communication program 52a to a downloaded update program. Or, the controller 51 determines whether a user has set timer on/off. If the user has set the timer on/off, the controller 51 updates the communication program 52a to the downloaded update program. Or, the controller 51 captures room temperature Ti and set temperature Tp, and determines whether a temperature difference ΔT calculated using the captured room temperature Ti and the set temperature Tp is greater than or equal to a threshold temperature difference Tth. If the temperature difference ΔT is greater than or equal to the threshold temperature difference Tth, the controller 51 updates the communication program 52a to the downloaded update program.