To provide an air conditioner which can be operated in the desired operating state of the user by letting the user have an energy saving feeling or an economical feeling by taking the electricity bill into consideration.

In a normal mode, the air conditioner is operated so that the bill for spent electricity may become nearly coincident with an expected electricity bill and the air conditioner is controlled so that the deviation of the temperature Ti in a room from a set temperature Ts may fall within the range of ±Tn until the temperature Ti reaches the set temperature Ts. In a saving mode, the number of revolutions of a compressor is reduced from that in the normal mode until the temperature Ti reaches the set temperature Ts so that the spend electricity bill may become lower than the expected electricity bill. In addition, the air conditioner is controlled so that the deviation of the temperature Ti from the set temperature Ts may fall within the range of ±Te (Te>Tn) which is larger than that in the normal mode. In a power mode, in addition, the air conditioner is operated by increasing the numbers of revolutions of the air conditioner and a fan so that the temperature Ti in the room may reach the set temperature Ts more quickly than the normal mode by ignoring the expected electricity bill.