To provide an interconnection system between a mobile phone and a peripheral mobile terminal the reliability of which is enhanced by preventing a missing peripheral terminal from being illegally used by a 3rd party even when the peripheral mobile terminal is missing.

The interconnection system is configured between the mobile phone 1 having a password code storage section 6 that stores a password used to identify its own and other party by which the password is set and the peripheral mobile terminal 2 that is connected to the mobile phone 1 to exchange data information or the like and has a password registration section 16 that registers in advance a password to identify the connectable mobile phone 1. While the system interconnects the mobile phone 1 and the peripheral mobile terminal 2, the mobile phone 1 transmits the password and the password registration section 16 of the peripheral mobile terminal 2 detects the coincidence between the received password and the password registered in the registration section 16 and the transmission reception of prescribed data information or the like is started when they are coincident.