To provide a controller of an air conditioner for avoiding errors in setting an address by enabling a simple setting of a group address on indoor units operated in a group.

A central controller A comprises a control input means 1, a group-setting mode for setting groups by dividing a plurality of indoor units B1, B2 and Bn into groups, a number temporary setting means for temporarily setting a prescribed group number, a group-setting means for setting all the indoor units belonging to the temporarily set prescribed group number as the units of a same group and a communication means 5. The indoor units, provided with an input means 11 comprising remote controllers C1, C2 and Cn, an address setting means 12 and a communication means 15 and transmission lines 6 for transmitting signals, are provided. In such a state that the group-setting mode is selected and the prescribed group number is temporarily set by the number temporary setting means, prescribed control inputs are performed by the input means to determine that all the indoor units, having had communication with the central controller, belong to the same group having the prescribed group number.