In mm-wave spectroscopy, the acousto-optic spectrometer (AOS hereafter) compares favourably with conventional spectrometers such as filter-banks or autocorrelators. Although its frequency resolution is limited to 20 kHz and its instantaneous bandwidth is limited to several hundred MHz, it has 103 resolvable points. Because of the simplicity and stability of the AOS, it is not difficult to construct and maintain a system of 104 resolvable points by the parallel operation of spectrometers. At Tokyo Astronomical Observatory (TAO) a new AOS has been constructed which is equipped with two different types of TeO2 AO deflectors and provides high resolution (38 kHz) or wide band (220 MHz) spectra. It has 1728 frequency channels (figure 1). Another AOS has been built at Kisarazu Technical College (KTC) for a CO survey at 115 GHz. It has 256 frequency channels and a bandwidth of 230 MHz (figure 2).