To provide a blow mold capable of clamping a parison without producing a clearance between the parison and an outer mold.

The outer mold 3 has the contact surfaces 34 and 35 coming into contact with the edge faces 24 and 25 in the axial direction of the stepped part of the parison 20 at the time of completion of mold clamping and the contact surfaces 34 and 35 are energized in the direction separated from the edge faces 24 and 25 by an energizing member 6 so as to form the clearances between the edge faces 24 and 25 and the contact surfaces 34 and 35 before the completion of mold clamping. A core 2 has the projection 9 projected toward the outer mold 3 and the outer mold 3 has a recessed part 10 in which the projection 9 is injected formed to its inner peripheral surface. The projection 9 and the recessed part 10 are respectively provided with inclined surfaces capable of being brought into slide contact with each other. The outer mold 3 is moved against the energizing force of the energizing member 6 by the slide contact of the inclined surface of the projection 9 and the inclined surface of the recessed part 10 on the way of mold clamping and the clearances become zero at the time of completion of mold clamping.