A mobile communication system provided with a home address holding function unit storing one home address, as a representative home address, from among a plurality of home addresses and the rest as subordinate home addresses, a position registration request function unit creating a representative address set and subordinate address sets with the representative home address and subordinate home addresses, acquired from the holding function unit, and a corresponding representative care-of address and subordinate care-of addresses and further sending a position registration request by only the representative address set, and a position registration function unit receiving the representative home address and subordinate home addresses acquired from the holding function unit, creating subordinate address sets from the representative address set relating to the position registration request, and registering the position of the representative address set simultaneously with the registration of the positions of the subordinate address sets.