A communication device for communicating with an external is connectable to a navigation apparatus. The navigation apparatus includes a display portion, an input portion for inputting memo information, an outgoing/incoming call determination portion, and a display control portion for controlling the display portion. The outgoing/incoming call determination portion determines whether or not the communication portion conducts an outgoing call and determining whether the communication portion receives an incoming call. When the outgoing/incoming call determination portion concludes that the communication portion conducts the outgoing call or that the communication portion receives the incoming call, the display control portion splits the display portion into a memo screen on which content of the memo information is displayed and a navigation screen.