To provide a PC card device and PC card system which is controlled optimally on the basis of the state of an information processing device to be connected.

This PC card device 1 is equipped with a connector serving as an interface 2, and can be mounted in a card slot of an information processing device through the connector. Control means 3 for controlling the PC card device detects the state of the information processing device connected to the connector, the type of a power source, the residual charge of a cell or battery when the power source is the cell or battery, the performance of CPU of the information processing device, the communication speed between the PC card device 1 and the information processing device, etc., and controls each part of the PC card device 1 on the basis of the detection result. Accordingly, even when the PC card device 1 is mounted in a different information processing device, the PC card device 1 can be optimally controlled in accordance with the information processing device in which the PC card device 1 is mounted.