[en] The branching ratio for ¹⁰C superallowed Fermi β decay has been measured accurately by a newly developed method. The result is 1.473±0.007 %. The Ft value is derived as 3065.4±14.7 sec, which is consistent with the Ft values determined accurately for heavier nuclei and with predictions of conserved vector current hypothesis. The method developed here can be applied to the high precision β-γ spectroscopy