A clad material of a clad steel pipe is disposed on at least one of an internal surface and external surface of a base material, the clad material having two lateral edges which are welded together to form the pipe. A thickness of the clad material at the two ends of the clad material in a lengthwise direction is predetermined at a first value, the first value which enables absorption of a discrepancy in thickness when connecting the clad steel pipe to another clad steel pipe; and wherein a thickness of the clad material at other parts other than the two ends is determined to be at a second value which is smaller than the first value.