An air conditioner and a heat exchanger therefor are provided. The heat exchanger may include a shell; an injection pipe to guide a heat source fluid to an inside of the shell; a first refrigerant tube formed with a first spiral tube; a second refrigerant tube formed with a second spiral tube having a radius larger than a radius of the first spiral tube; and a discharge pipe to which the heat source fluid heat-exchanged with a refrigerant is discharged. The first refrigerant tube and the second refrigerant tube may be connected in parallel, and the second spiral tube may have a larger pitch between turns and a smaller number of turns than the first spiral tube. The heat exchanger may provide a simple structure and a high heat-exchange performance.