To write control information into a recording medium with a high density by using signals of the audible frequency band, without compressing the storage region of aural infraction.

An equipment 2 to be controlled is controlled by using the control information written into a part of the region which records voice information in the recording medium 1. The control information written into the recording medium 1 in the form of modem signals, converted in the audible frequency band, is read out using a reading device 3 and reproduced into control signals in a signal reproducing section 4, so that its content is interpreted by a signal decoding section 5. A control output section 6 controls the instrument 2, in accordance with the content of control interpreted by the signal decoding section 5. Since modem signals are higher in data density than DTMF signals, one can write control information into the recording medium 1, without compressing the recording region of aural information.