A steam generator includes a generator body including an inlet through which fluid is introduced and or outlet through which the fluid is discharged, a first flow channel providing a flowing path for the fluid is introduced into the generator body through the inlet, a second flow channel to guide the fluid from the first flow path to the outlet, and a heater to heat the generator body, the heat of the generator body being exchanged with the fluid guided through the first and second flow channels, and greater amount of heat being provided at the first flow channel than the second flow channel.