Disclosed is a steam oven to cook food in a cooking chamber by use of steam. More particularly, disclosed is a steam generator of a steam oven, which can simplify the configuration of a device required to generate steam and is detachably attached to a cabinet to assure easy cleaning and washing thereof. The steam generator includes a single body having an inner space divided into a water supply compartment and a boiler compartment by a partition, the water supply compartment having a water pouring hole, and the boiler compartment having a heater and a steam discharge hole. Also, a water supply passage is defined between the water supply compartment and the boiler compartment. This configuration has the effects of achieving improved workability and reduced manufacturing costs of the steam generator and also, of overcoming a limit in the inner volume of a cooking chamber of the steam oven.