In order to measure frequency responses of O/ E conversion devices such as photodiodes (PDs), we developed a measurement instrument named lightwave frequency response analyzer (LFRA). LFRA, which is based on a heterodyne technique utilizing an optical modulator, provides precise measurement solution with cost effective instrument. Measured results of two individual LFRAs show standard deviations less than 0.15 dB and maximum instrument difference less than 0.7 dB.