Abstract: Analog signals of multiple channels received by a terminal are passed through a filter, converted into digital signals by an A/D converter, and are stored temporarily on a RAM. The digital signals are then stored in a recording data section at a particular sector of a magneto-optic disk, while recording an ID number, real-time information on time to start and end recording, event information, trigger information, and so on in a condition data section at the identical particular sector as an index of a search. Upon the search for data, only the condition data section is searched for, thereby permitting a random access and search at a high speed.