An active feedback loop is provided in a switched-capacitor circuit to automatically cancel both junction and sub-Vth channel leakage. The electromagnetic flow meter has first and second detection resistors which are connected in series to ends of the exciting coil via the switching elements, respectively, wherein a midpoint of the first and second detection resistors is grounded to set a voltage of the midpoint as a circuit reference voltage. The length of the first opening is shorter than that of the second opening. When the portable computing device is in a closed position, the space between the first and second inward edge formations defines a groove formation around the periphery of the portable computing device.