A tubular-member lock mechanism includes a cylindrical housing to which a tubular member having an engagement portion at one end is mounted, and a lock member for engaging or releasing the housing and the tubular member. The housing includes a lock-member guide wall turnably guiding the lock member, at least two sliding surfaces with different inclinations wherein a tip portion of the lock member slides by turning the lock member, and a slit through which one portion of the lock member passes to engage the engagement portion of the tubular member mounted to the housing. The lock member, at a standby/lock position, engages the engagement portion formed on an outer periphery of the tubular member, and the lock member, at a release position where a rotational load is applied, spreads by the sliding surfaces having the different inclinations releases the engagement portion of the tubular member.