A joining state determination method includes: acquiring member front end imaging data of a band-shaped member; acquiring member joint imaging data of the band-shaped member; calculating a matching rate indicating a degree of coincidence of the acquired member joint imaging data with member front end registration data registered based on the acquired member front end imaging data; and determining that the longitudinal ends of the band-shaped member are properly joined, in the case where the calculated matching rate is either not greater than a predetermined threshold or less than the predetermined threshold.