A container attachment device includes a toner container, an attached part for the toner container and a displacement sensor. The displacement sensor faces to the toner container to detect electrostatic capacity according to the toner. The attached part includes a cover opening/closing an opening of the toner container. The cover closing or opening the opening faces to the displacement sensor, and the cover opening or closing the opening is away from the displacement sensor. The displacement sensor detects the electrostatic capacity varying among a first condition opening the cover and detaching the toner container, a second condition closing the cover and detaching the toner container, a third condition opening the cover and attaching the toner container, and a fourth condition closing the cover and attaching the toner container. In the third or fourth condition, the displacement sensor detects the electrostatic capacity according to a toner quantity in the toner container.