The present invention provides a compact tube clamping device 50 with a simple structure and used suitably for a hydraulic pressure tester for inspecting quality of an electric resistance welded tube. To achieve this object, a lifting/lowering base 52 including a tube support body 55 on itself is provided onto a fixed base 51 to be able to lift and lower. Clamp claws 56 are mounted in positions, between which the tube support body 55 of the lifting/lowering base 52 is sandwiched, to be able to turn. A claw drive body 58 for lifting and lowering independently of the lifting/lowering base 52 is provided in the lifting/lowering base 52. Opposite side portions of the claw drive body 58 are connected to the opposite clamp claws 56 by links 59 so as to turn the opposite clamp claws 56 in closing directions by lowering with respect to the lifting/lowering base 52. Both of a first drive mechanism 53 for driving the lifting/lowering base 52 for lifting and lowering and a second drive body 54 for driving the claw drive body 58 for lifting and lowering are provided to the fixed base 51. Because a lowering stroke of the claw drive body 58 necessary for closing operations of the clamp claws 56 is partially born by lifting of the lifting/lowering base 52 in transferring the tube, the lowering stroke of the claw drive body 58 for opening and closing the clamp claws 56 can be suppressed.