An adjustment assistance device is attached to a galvanometer scanner at a laser output side of the galvanometer scanner and used to adjust a tool coordinate system of the galvanometer scanner. The adjustment assistance device includes a light-receiving member having a light-receiving surface, which is at least one flat surface; and a connecting member that connects the light-receiving member to the galvanometer scanner and that enables the light-receiving surface to face a laser output port of the galvanometer scanner with a predetermined distance therebetween. The light-receiving member includes a light-receiving mark portion on the light-receiving surface, the light-receiving mark portion being a mark used to quantify a relative positional difference between a reference light-receiving position for light output from the laser output port and an actual light-receiving position at which the light output from the laser output port is received.