We demonstrate high-speed terahertz (THz) time-domain spectroscopy based on electronically controlled optical sampling (ECOPS). The ECOPS system utilizes two synchronized Ti:sapphire femtosecond lasers with a $100\mathrm{MHz}$ repetition frequency. The time delay between the two laser pulses is demonstrated to be rapidly swept at a scan rate of $1\mathrm{kHz}$ on a time delay window of $77\mathrm{ps}$ by using an external offset voltage applied to a locking electronics. It is shown that a THz pulse can be exactly measured by ECOPS, as is done by asynchronous optical sampling (ASOPS), and the measurement time is shortened by a factor of 50 by using ECOPS compared with ASOPS in the case of employing $100\mathrm{MHz}$ repetition-rate lasers.