A developing device includes a developer container having a developer supply opening and a developer storage section, so that developer is supplied from the developer container to the developer storage section through the developer supply opening. The developing device further includes a developer guide member disposed below the developer supply opening along a longitudinal direction of the developing device, and a developer delivery member disposed in the developer guide member for delivering developer supplied through the developer supply opening in a longitudinal direction of the developer guide member. The developer guide member has a wall portion having a shape so that developer flows out the developer guide member in a substantially uniform amount along the longitudinal direction of the developing device.