An image forming apparatus includes a housing, a container body, and an electrostatic capacitance sensor. The container body contains a liquid and is placed on a ground surface which is a part of the housing. The electrostatic capacitance sensor detects a change in capacitance between a side surface of the container body and the ground surface to determine a change in quantity of the liquid in the container body. The top surface of the container body is a part of the housing. The top surface and the ground surface are in electrically conductive state, a distance between the top surface and the electrostatic capacitance sensor is longer than a distance between the ground surface and the electrostatic capacitance sensor, or the top surface and the ground surface are electrically insulated, or the top surface is opened.