PURPOSE: To secure independent of size of neck diameter of measuring tube and shape of cut deformation section by arranging movable vice in opposition to fixed vice having V shape surface respectively, and securing the core measuring tube by elastic force applied by movable vice.

CONSTITUTION: Pressurized water is delivered within a cylinder 10 by passing through hydraulic leading hole 27, and depressed the piston 12 against coil spring 19. The movable vice 21 and the fixed vice 24 opposing thereagainst form V shape surface. When the distance between the vices forms the maximum, moving to above the core measuring tube 25. By releasing hydraulic pressure, it is placed between the movable vice 21 actuated by coil spring 19 and the fixed vice 24. This enables to hold accurately regardless of pipe size without showing error operation since it is operated by the spring force during holding time.