To provide a resistance welded tube of high carbon steel, excellent in hot workability and improved in an ultrasonic flaw detection yield.

This resistance welded tube is constituted of a hot rolled high carbon steel plate obtained by applying hot rolling to a high carbon steel slab which is prepared by continuously casting a high carbon steel having a composition consisting of 0.3-0.8% C, 0.15-0.35% Si, 0.3-1.5% Mn, ≥0.012% P, ≤0.040% S, 0.035% Al, and the balance Fe with inevitable impurities and in which the degree of segregation of P, determined by dividing the concentration of P in the central segregation part by the ladle-analytical P value, is regulated to ≤10.0. By this method, hot cracking can be inhibited and a reduction in the yield of ultrasonic flaw detection can be decreased.