Disclosed herein are a water supply device, and a steam supply device and a cooking appliance comprising the same. The water supply device comprises a slider being accommodated in a housing the front surface of which is open, in a way that the slider is movable in a front-rear direction, and a water tank being installed in the housing in a way that the water tank comes in and out of the housing in the front-rear direction and connecting to the slider to move forward together with the slider, and the slider is provided apart from the water tank.