A computer apparatus which integrates at least two or more services of user management domains has a processor, a memory and an interface. The processor receives an access request, specifies an access source domain, specifies an access target domain, and judges whether the specified access source domain matches the specified access target domain. If the access source domain is different from the access target domain, the processor extracts a user ID of the specified access source domain from the received access request, and refers to ID conversion information indicating correspondence of user IDs between the user management domains whose services are integrated to convert the extracted user ID of the access source domain into a user ID of the specified access target domain. Thus, loads of configuration at the time of service integration are reduced.