A locking mechanism for a tubular body, comprising: a tubular housing), the tubular body having an engagement portion and being mounted on at least one end of the tubular housing, and a locking member that locks and releases the housing and the tubular body, wherein the locking member is mounted to the housing to be able to move in an outer diameter direction by a tapered portion of the tubular body when the tubular body is inserted; and the housing includes a slit formed to pass a curved portion bent in an inner diameter direction disposed at a leading-end side of the locking member and to lock with the engagement portion of the tubular body mounted on the housing; a gap is disposed between the curved portion and an end portion of the slit positioned at a side in an opposite direction to the leading-end side of the locking member, so as not to contact therebetween while at least the locking member is moving, or the locking member is mounted to the housing to be able to move in the outer diameter direction, and the housing includes a slit formed to pass the curved portion bent in an inner diameter direction disposed at a leading-end side of the locking member and to lock with the engagement portion of the tubular body mounted on the housing; and also, the housing includes a guide for widening the curved portion toward an outside when the locking member is moved to the outer diameter direction at least at a time a locked state is released, characterized in that the guide includes an oblique sliding surface extending from the outer surface of the housing that enables the leading-end portion of the locking member to slide toward the outside in the diameter direction, when the locking member moves to the outer diameter direction to the housing, or when moving from a position after moving to the outer diameter direction, to the inner diameter direction. a tubular housing), the tubular body having an engagement portion and being mounted on at least one end of the tubular housing, and a locking member that locks and releases the housing and the tubular body, wherein the locking member is mounted to the housing to be able to move in an outer diameter direction by a tapered portion of the tubular body when the tubular body is inserted; and the housing includes a slit formed to pass a curved portion bent in an inner diameter direction disposed at a leading-end side of the locking member and to lock with the engagement portion of the tubular body mounted on the housing; a gap is disposed between the curved portion and an end portion of the slit positioned at a side in an opposite direction to the leading-end side of the locking member, so as not to contact therebetween while at least the locking member is moving, or the locking member is mounted to the housing to be able to move in the outer diameter direction, and the housing includes a slit formed to pass the curved portion bent in an inner diameter direction disposed at a leading-end side of the locking member and to lock with the engagement portion of the tubular body mounted on the housing; and also, the housing includes a guide for widening the curved portion toward an outside when the locking member is moved to the outer diameter direction at least at a time a locked state is released, characterized in that the guide includes an oblique sliding surface extending from the outer surface of the housing that enables the leading-end portion of the locking member to slide toward the outside in the diameter direction, when the locking member moves to the outer diameter direction to the housing, or when moving from a position after moving to the outer diameter direction, to the inner diameter direction.