The accuracy of HF radar measurement in the Tsushima Strait is investigated. A comparison between radial velocities measured by HF radar and acoustic Doppler current profiler (ADCP), which provides an upper bound of HF radar measurement error, shows that the root-mean-square (RMS) velocity difference obtained from the principal component analysis is 6.62~11.3 cm s-1. A comparison of velocities measured by two facing HF radars, which provides a lower bound of HF radar measurement error, shows that the variance error of hourly radial velocity is 5.75~13.3 cm s-1. The bias error of HF radar measurement is also found to be reasonably small through a comparison of tidal ellipses estimated from 1 year of HF radar data with those from 5 years of ADCP data. These results suggest that the variance error of HF radar measurement is the dominant source of the velocity difference found between ADCP and HF radar.