A coupling instrument is provided that can easily attach or detach a main body to or from a cleaning part in a cleaning device. The coupling instrument includes a first coupling member including a bulging part having a slant part. A side peripheral part of the slant part is tapered toward a tip thereof. A first protruding part is formed in a protruding manner around the bulging part. The coupling instrument further includes a second coupling member including a fitted part in which the bulging part can be loosely fitted, and a second protruding part formed in a protruding manner around the fitted part. The second protruding part is adjacent to the first protruding part; and the second coupling member has a plurality of engaging parts arranged around the fitted part.