An auxiliary member is an auxiliary member that assists in mounting a roll body, which is formed by winding a sheet into a roll shape on a core tube, onto a shaft of a printing apparatus. The auxiliary member includes a cylindrical main body insertable into the core tube, a laser irradiation unit that irradiates laser light from a leading end surface of the main body, and a switch that switches between irradiation and stopping of the laser light from the laser irradiation unit.