To obtain a sense of unity with a host device which is operated through an input device by varying a feeling of operation given to human fingers for operation according to the operation state of the input device.

An operation mechanism 50 varies the capacity of a chamber 10 directly or indirectly by using physical variation generated by operation with human fingers as an external force. An operation information generating means 60 detects the physical variation corresponding to the operation state of the operation mechanism 50 and converts it into an electric signal. This electric signal is transmitted to the host device 100 through a transmitting circuit 70 as the interface part between the input device 1 and host device 100. An operation feeling control signal outputted properly by the host device 100 is inputted to a flow resistance varying means through a receiving circuit 80. The flow resistance varying means 40 uses the operation feeling control signal as a driving signal to vary how easy fluid 20 in a contraction conduit 30 flows. Consequently, the resistance feeling of the operation mechanism 50 for varying the capacity of the chamber 10 varies.