In step S320, the system controller 50 determines whether a period of time from when Touch-Down is performed in step S317 to when the touch is released in step S319 is smaller than the predetermined period of time α. Specifically, it is determined whether the time t in which the measurement is started in step S318 is smaller than α. When it is determined that t is smaller than α, the process proceeds to step S321, and otherwise, the process proceeds to step S305.

In step S321, the system controller 50 determines whether the coordinate (x1, y1) of the first tap operation obtained in step S313 is close to the coordinate (x2, y2) of the second tap operation obtained in step S318. Specifically, it is determined whether the coordinates of the tap operations which are consecutively performed are close to each other. If a distance between the coordinate of the first tap operation and the coordinate of the second tap operation is within 0.5 cm or 0.3 cm, for example, it is determined that the coordinates are close to each other. When it is determined that the first tap operation and the second tap operation are close to each other, the process proceeds to step S322, and otherwise, the process proceeds to step S305.