Seamless steel pipe and manufacturing method of same

Provided is a seamless steel pipe in which a yield strength of 555 MPa or more and excellent SSC resistance can be stably obtained. The seamless steel pipe, as a mass%, comprises C: 0.02-0.15%, Si: 0.05-0.5%, Mn: 0.3-2.5%, Al: 0.01-0.10%, Ti: 0.001-0.010%, N: 0.007% or less, Cr: 0.05-1.0%, Mo: 0.02% or more and less than 0.5%, Ni: 0.03-1.0%, Cu: 0.02-1.0%, V: 0.020-0.20%, and Ca: 0.0005-0.005%, wherein a carbon equivalent Ceq is 0.430% or more and less than 0.500%, wherein the structure has a tempered martensite or tempered bainite as the main phase from a surface layer to a thickness, wherein a size of a prior austenite grain is less than 6.0 in terms of grain size number according to ASTM E 112-10, and wherein, between a position of 1 mm from the inner surface and a position of 1 mm from the outer surface, the Vickers hardness is 250 Hv or less and the yield strength is 555 MPa or more.