A toner replenishing device includes a sub hopper (toner container), a toner detection sensor, an agitator, and a paddle. The sub hopper contains toner. The toner detection sensor is located on a wall surface in the sub hopper and detects whether toner remains at a height at which it is located. The agitator rotates in the sub hopper to clean the detection surface of the toner detection sensor. The paddle serves as a toner collecting unit that collects toner to the vicinity of the detection surface of the toner detection sensor in the sub hopper.