To obtain a chlorinated vinyl chloride resin excellent in both heat resistance and processability by chlorinating a vinyl chloride resin whose surface and inside are each in a specified state.

This chlorinated resin is obtained by chlorinating a vinyl chloride polymer which has a BET specific surface of 1.3-8cm2/g and of which the ratio of peaks at the 1S bond energy value (eV) between carbon and chlorine elements [(chlorine element peak)×2/-carbon element peak] is above 0.6 when the surface of the resin particle is analyzed by ESCA (electron spectroscopy for chemical anylysis). A known method for chlorination can be used as it is for the chlorination.