First detection information related to electrical connection between each row signal line and each column signal line is received from a key matrix circuit (S101). Based on the first detection information, it is determined whether a possibility exists that a user has pressed at least three key switches simultaneously and electrical connection between signal lines for a key switch that has not been pressed has been erroneously detected (S108). Information in accordance with key switches pressed by the user is output based on the first detection information when the determination is negative (S109), whereas output of information based on the first detection information is blocked when the determination is positive.