A developer supply mechanism is composed of: a developer supply path one end side of which is opened upward and which guides the developer in substantially a vertical direction; a convex portion that is formed on a wall surface of the developer supply path; a coil spring that is disposed in the developer supply path, stretchable and shrinkable in a longitudinal direction of the developer supply path, pressurized to the convex portion in a natural-length state, stretched toward one end side of the developer supply path when the convex portion is hooked on between pitches by a circumferential-direction rotation, and is given a horizontal-direction movement to leave the convex portion when coming off the convex portion; and a drive portion that is connected to the coil spring at the other end side of the developer supply path and rotates the coil spring in a circumferential direction of the coil spring.