The present invention provides a checking tool for a tube coupler with which it is possible to visually check an attachment state of the tube coupler. A checking tool 10 for a tube coupler according to the present invention is a checking tool configured to be attached to a tube coupler 30, the tube coupler being formed of a first coupling piece 31 and a second coupling piece 35 hingedly connected to each other so as to be able to be opened and closed, being configured to couple tubes to each other with use of the first coupling piece and the second coupling piece, and having hook pieces 33 and 37 that are provided protruding from outer circumferential surfaces of the first coupling piece and the second coupling piece. The checking tool includes a pair of longitudinal frames 11 that conform to an outer circumferential surface of the tube coupler, a first lateral frame 12 that connects end portions at one end of the pair of longitudinal frames to each other, a second lateral frame 16 that connects end portions at the other end of the pair of longitudinal frames to each other, a first claw piece 13 that is provided protruding from the first lateral frame toward the second lateral frame, and a second claw piece 17 that is provided protruding from the second lateral frame toward the first lateral frame.