PURPOSE: To provide a core bar for bending a pipe in an apparatus enabling the bending without occurrence of the shortage of oil and smoothly bending the pipe without deformation of crush, etc., due to elongation at the position bringing the core bar for bending the pipe into close contact with the inner surface of the pipe.

CONSTITUTION: Plural grooves 24 having 0.1-1.5mm width W, desirably 0.2-0.8mm width, so that the working oil can be held and the breakage by bending force at the time of bending is prevented, are arranged in the whole periphery of the core bar 14 at the position bringing into close contact with the inner surface of the pipe.