In a digital filter device which filters a plurality of signals by a single digital filter, an input data memory stores the input data strings generated by computing processors, and a digital filter reads the input data strings in a predetermined sequence to be filtered and generates output data strings. An output data memory stores the output data strings, and a data processor reads the output data strings in a predetermined sequence to be processed. Furthermore, a filter memory and coefficient memories respectively store data-under-calculation and a filter coefficient in a delay circuit included in the digital filter.