To provide a method for managing the copies of a shared data file held in the computer systems that can be connected together via a mobile communication network by preparing a step where the shared file copies are changed based on a changing sequence whose collision problems are already resolved.

The copies 420 of a shared data file held in plural computer systems that can be connected together via a mobile communication network 460 are managed. This management method includes a step where the record of change given to every copy of the shared data file is held, a step where the records held to other copies of the data file are taken out via the connection secured to the network 460, a step where the taken-out records are merged in each other and a changing sequence is generated, a step where a rule defined previously is applied to the changing sequence to resolve the collision problems in the changing sequence, and a step where the copies of the data file are changed.