PURPOSE: To prevent the strain aging embrittlement of a part affected by heat of post-annealing and to improve the toughness of an electric welded steel pipe by adding B to steel by an adequate amount to N in the steel and further adding ≥ one kind of Nb, V.

CONSTITUTION: The composition of the material of an electric welded steel pipe is composed of, by weight, ≤0.4% C, ≤0.8% Si, 0.3W1.8% Mn, 0.01W0.10% Al, 0.0030W0.0150% N, 0.0006W0.0090% B, ≥1 kind of 0.01W0.10% Nb, 0.01W0.15% V, and the balance Fe with inevitable impurities while regulating the ratio of B/N to 0.2W0.6. Thus, the strain aging embrittlement of a part affected by heat of post-annealing is prevented, and a uniform toughness value is provided in the peripheral direction of the pipe.