A control program signal demodulating device comprises a control program demodulator for obtaining a demodulated output of a control program signal from a signal which is reproduced from a rotary recording medium which is recorded with at least the control program signal together with a video signal, where the control program signal indicates a control program including input and output commands and internal processing commands of an external device such as a computer which has a discriminating function and is coupled to a player which plays the rotary recording medium, a memory circuit for at least temporarily storing the demodulated output of the control program demodulator and producing the stored demodulated output, a selecting circuit for selectively producing data received from the memory circuit in response to a transmission request, an interface circuit for transmitting the data which is produced from the selecting circuit to the external device, and for receiving one or a plurality of control commands from the external device, and a command analyser for decoding one or a plurality of control commands received from the interface circuit, and for generating a signal which controls the operation of the player or a signal which requests transmission with respect to the memory circuit and the selecting circuit.