PURPOSE: To control the operation of an air conditioner for its stop by changing brightness in a room.

CONSTITUTION: There are an indoor unit body 1, a front panel 2, a wind direction control plate 3, a light receiver 4 for a remote control signal, a sensor 5 for detecting a brightness in a room, and an operation mode changeover switch 6. Further, a controller (microcomputer) is provided behind the panel 7. The controller has, in addition to a memory for storing a criterion reference value of brightness in a room, a memory for storing operation modes, a comparator for comparing the brightness, a timer, etc. When the switch 6 is, for example, opened, an operation in a normal operation mode can be continued. When the switch 6 is closed, the normal operation mode is automatically switched to an operation mode, when the brightness in the room becomes a reference value or lower, at the time of sleeping. Then, when a predetermined time is elapsed, the operation of an air conditioner is automatically stopped.