The chemical composition of the seamless steel pipe contains Cr: 15.00 to 18.00% in mass % and satisfies Formulae (1) and (2). Furthermore, in the microstructure, (I) a total volume ratio of ferrite and martensite is 80% or more, with the balance being retained austenite of a volume ratio of 20% or less, (II) the number of intersections NTL in the L-direction observation field of view is 38 or more and NTL/NL is 1.80 or more, and further (III) the number of intersections NTC in the C-direction observation field of view is 30 or more and NTC/NC is 1.70 or more.

156Al+18Ti+12Nb+11Mn+5V+328.125N+243.75C+12.5S≤12.5  (1)

Ca/S≥4.0  (2)