To obtain a low alloy heat resistant steel excellent in weldability as well as in high temp. strength and useful, e.g. for chemical reaction vessels, industrial non-heat-resistant members, and further various high temp. equipment parts while obviating the necessity of the addition of large amounts of alloying elements.

This steel has a composition which consists of, by weight, 0.05-0.25% C, 0.1-1.0% Si, 0.2-2.0% Mn, 0.01-0.5% Cu, 0.01-1.5% Ni, 0.01-0.7% Cr, 0.01-0.7% Mo, 0.001-0.07% V, 0.002-0.01% N, one or ≥2 kinds among 0.001-0.025% Al, 0.001-0.05% Nb, and 0.001-0.025% Ti, and the balance Fe with inevitable impurities and in which the value of N*, defined by N*=N-(0.4Al +0.15Nb+0.3Ti), is regulated to 0.0005-0.005%.