To provide a martensitic stainless steel seamless steel tube in which the delayed fracture of the part to be subjected to impact working is hard to occur, and which has no internal defects, and to provide a method of producing the same.

The steel tube has a composition comprising 0.15 to 0.22% C, 0.1 to 1.0% Si, 0.10 to 1.00% Mn, 12.00 to 14.00% Cr and one or more kinds of metals selected from V, Nb and Ti of 0.005 to 0.200%, respectively, and 0.0005 to 0.0100% B, and in which the following inequalities (1), (2) or (3), (4) and (5) are all satisfied: the inequality (1) is expressed by C*+10N*≤0.45; the inequality (2) is expressed by H1≤-0.003(C*+10N*)+0.0016; the inequality (3) is expressed by H2≤-0.0018(C*+10N*)+0.00096; the inequality (4) is expressed by Cr*≤9.0; and the inequality (5) is expressed by S≤0.088N*+0.00056. In the inequalities, C* is an effective solid solution carbon content; N* is an effective solid solution nitrogen content; Cr* is a Cr equivalent; H1 is a residual hydrogen content in the steel tube after tube making; and H2 is a residual hydrogen content in the steel tube after heat treatment. The tube making is made possible without the occurrence of internal defects by controlling a crossed angle and an inclined angle on piercing rolling.