An image forming apparatus includes a main body, a print engine, a detection circuit, a switch, and a processor. The print engine is located within the main body to form an image by using a toner. The print engine generates waste toner. A waste toner container is detachably mountable to the main body of the image forming apparatus and collects the waste toner. The detection circuit includes a toner amount detection sensor to output a voltage value associated with an amount of waste toner in the waste toner container and a switch to selectively output the voltage value depending on whether the waste toner container is mounted or detached. The processor determines whether printing is available based on the voltage value outputted from the detection circuit.