A spark plug cap for facilitating the fittingdetaching operation of a spark plug with a built-in pressure sensor, and a method of easily fitting the spark plug with a built-in pressure sensor are provided. The conveyer contacts the sheet placed on the first placement unit, when the lifting plate is in the approximate position, and conveys the contacting sheet into the conveyer path. The second sidewall has a length shorter than that of the first side wall, and has a tapered bottom end that includes a bottommost end, and an inclined edge that extends upwardly from the bottommost end of the second sidewall. According to one aspect of the present invention, a clearly discernible feedback is provided to clearly indicate engagement between the ground-engaging member and the sole. The detonation wave propagates the length of the at least one detonation tube and exits the open end of the at least one detonation tube as a sound wave. If the voltage difference between the main supply voltage and the battery voltage is smaller than a lower voltage level, the controller will increase the voltage level of the adjusting signal so as to increase the power supplied by the power supply device.