An air conditioner including a first filter; a second filter located downstream of the first filter; a dust amount sensor located upstream of the first filter and having a hole through which dust passes, the dust amount sensor configured to transmit, per unit of time, each of a first total, which is an amount of dust in a first size range, and a second total, which is an amount of dust in a second size range smaller than the first size range, of the dust passing through the hole; and a controller configured to output a service signal for the first filter if the accumulated value of the first total transmitted from the dust amount sensor exceeds a first set value, and output a service signal for the second filter if the accumulated value of the second total transmitted from the dust amount sensor exceeds a second set value.