In the developing apparatus (1) including a developing bath (2) and a toner transport pipe (3) for supplying toner to the developing bath (2), a toner supply portion opening/closing mechanism is provided, that includes a shutter member for opening and closing a toner supply port of the toner transport pipe (3) that is contained in a base portion (12) of the toner transport pipe (3), a shaft (30) for moving the shutter member back and forth in a longitudinal direction of the developing bath (2), a second spring member (33) provided such that the shaft (30) is inserted therein, a first spring member (26) for supporting the shaft (30) detachably to the shutter member (20) through its extension and contraction, and a lever member (25) for extending and contracting the first spring member (26) through its releasing and closing.