A multi-channel digital event recording system with automatic event detection and location has been developed by using personal computers with clock frequency of 8 MHz. The system is designed to record seismic signals of more than 100 input channels with a sampling frequency of 150 Hz. The sampled data are written on a hard disk with a cassette streamer, which can copy all the data in the hard disk to a cartridge tape. The capacity of the hard disk is 20 Mbytes, which corresponds to waveform data for 40 events. Although a personal computer is used, it takes only 2 min to pick P and S wave arrivals of 27 stations and to calculate a hypocenter location. The present personal computer system was used in the seismic observation of the 1986 Joint Seismological Research in the Western Nagano Prefecture. Waveform data of about 2,800 events were recorded during the observation period of 52 days, and 1,264 events that occurred in the aftershock area were precisely located in the seismic observation. Hypocenters of about 2,000 events, including about 1,600 local events, were determined automatically by using the data played back from the streamer tapes.