Disclosed is an air conditioner with functions for deciding room shape by determining, based on a temperature difference, information between the room's floor and walls occurring during operation, a human body detection position log, and a capacity zone of the air conditioner. In an embodiment, an infrared sensor detects a temperature of an area of the room by scanning the area and a control unit acquires thermal image data of the area scanned by the sensor and then controls the air conditioner based on the thermal image data. The control unit sets a boundary line between a wall and floor of the room at a position on the thermal image data, calculates a temperature difference between vertically adjacent pixels located above and below the boundary, corrects a position of the boundary based on temperature difference, and determines that areas parted by the boundary correspond to the wall and floor, respectively.