A volume management system, a managing computer, a host, and a volume management method being capable of regulating the authorities of users and avoiding misoperations are provided. The volume management system comprises a storage having volumes served as a storage region, a managing computer, and a plurality of hosts used by users obtaining an operation authority over the volume. Two or more users can use an identical volume. Upon obtaining an operation content of one user for at least one of the volumes over which two or more users have the operation authority, the managing computer determines from an attribute of the volume and the operation authority of the two or more users over the volume whether the operation content is executable. When the operation content is not executable, the operation content is restrained.