Broadband and ultrafast frequency sweep signal generation technique has been desired in radar applications as well as signal sources for ultra-wideband wireless communication . Optical signal generation technique is a possible candidate for ultra-broadband signal generation although all electrical one is difficult to apply due to its bandwidth. In conventional modulation technique, however, an extinction ratio of an optical modulator, which is typically around 20 dB, could require optical filters for rejection of unnecessary harmonics and tones. High extinction ratio (HER) optical modulator with a structure of dual-parallel Mach-Zehnder interferometer (DPMZI) achieved the extinction ratio of 70 dB [2, 3]. Thus, simple and robust system configuration without optical filters can be possible with the modulator. In this paper, we demonstrated ultrafast and broadband electrical frequency chirped signal generation with the bandwidth of 12.8 GHz and the repetition rate of 20 MHz using the HER modulator.