When a select lever is in a drive range, a microcomputer reads a value of an output voltage by a switch-operation-signal output circuit after detecting that both shift-up switch and shift-down switch are substantially simultaneously turned on, checks whether or not the output voltage by the switch-operation-signal output circuit is the output voltage indicating that the switch after a predetermined time has elapsed is in a normal condition, and only when the output voltage is such an output voltage, permits a manual mode of an automatic transmission and when the output voltage is not such an output voltage, cancels the manual mode.