Card reader and foreign matter detection method

A foreign matter detection method for a card reader comprising a main body part including a card conveyance path in which a card inserted into an insertion port is conveyed, a shutter member structured to move between a closed position which closes the card conveyance path and an open position which opens the card conveyance path, and a first capacitance sensor provided in the main body part and structured to detect that an object is present in the card conveyance path,

• the foreign matter detection method comprising:
• calculating a first output difference which is a difference between an output of the first capacitance sensor in a first state in which the shutter member is in the closed position and the output of the first capacitance sensor in a second state in which the shutter member moves from the first state to the open position and then moves to the closed position, calculating a second output difference which is a difference between a maximum output of the first capacitance sensor in a period from the first state to the second state and the output of the first capacitance sensor in the second state, and determining that an object other than the card is installed in the card conveyance path when the first output difference is a predetermined first threshold or more, and the second output difference is less than a predetermined second threshold.