1. A virtual storage management method in a loosely coupled multi-processor system in which individual processors are each individually connected to a respective physically addressable physical main storage, and use virtually addressable virtual storages and share a common physically addressable external storage, the method comprising the steps of: using physical addresses, with a first processor included in said multi-processor system, i) copying first data from a first main storage connected to said first processor into said shared external storage, and ii) storing a mapping table in said shared external storage, said mapping table including storage positional information of said first data stored in said first main storage dispositive of where said first data is stored in said shared external storage; with a second processor that is one of the processors included in said loosely coupled multi-processor system, i) addressing a virtual storage location in the multi-processor system using a first virtual address ii) detecting that an area corresponding to the virtual storage location addressed by said first virtual address has not been allocated to a second main storage connected to said second processor, and iii) with the second processor and using physical addressing, copying the first data into said second main storage from said shared external storage corresponding to said virtual storage location, wherein the steps of addressing, detecting and copying include steps of referring to said mapping table by the second processor and obtaining the storage positional information of said first data in said shared external storage; and, with said second processor, accessing the first data copied into said second main storage.