A new method for surface treatment of copper vacuum chamber has been developed to easily obtain lower photodesorption coefficients due to synchrotron radiation at low cost. An oxygen‐free high‐conductivity (OFHC) copper test chamber is extruded and degreased, then the inner surface is cut by broaching. The length of the test chamber is 300 mm and the outer diameter is 65 mm. For comparison, three OFHC copper test chambers are manufactured with different surface treatments. These treatments are (1) acid cleaning (pickling in a mixed solution of HNO3 and H2SO4, followed by passivation in a chromic acid with H2SO4), (2) broaching with oil, and (3) oil‐free broaching. These test chambers were exposed to synchrotron radiation with 4 keV critical energy from BL21 beamline at the Photon Factory 2.5 GeV storage ring at KEK. The photodesorption coefficients (N2 or CO equivalent) for the chamber treated with oil‐free broaching and for the chamber treated with acid cleaning are almost the same. However the decreasin...