A water supply tank unit, attached to a heating apparatus having a moistening function, comprising an open/close member biased in a direction of departing from a unit body attached to the heating apparatus, and a water supply tank held in the open/close member so as to be attachable/detachable, wherein the water supply tank and the open/close member have protrusions respectively so that the protrusions climb over each other and are locked to each other in a process of attaching/detaching the water supply tank.