A remaining toner amount detection device includes four electrodes and a controller. Each electrode has an arc shape along an outer circumferential surface of a toner bottle, and the four electrodes are spaced a certain distance apart in a circumferential direction so as to surround the toner bottle. The controller detects a remaining toner amount inside the toner bottle by using the four electrodes. The controller determines whether at least one of a first electrostatic capacity value between one pair of adjacent electrodes and a second electrostatic capacity value between the other pair of adjacent electrodes falls within a threshold range. In response to determination that at least one of the electrostatic capacity values falls within the threshold range, the controller detects a remaining toner amount inside the toner bottle based on an electrostatic capacity value, and outputs the detected remaining toner amount.