An air-conditioner wherein the lubrication oil flowing through the refrigerant passage along with the refrigerant is reliably returned to the refrigerant compressor by having the refrigerant piping at the suction side of the compressor comprised of a first refrigerant piping and a second refrigerant piping connected in series with the same, the large diameter first refrigerant piping extending from a high position to a low position and the relatively small diameter second refrigerant piping extending in substantially the horizontal direction.
