PURPOSE: To perform address conversion at high speed, by obtaining a real address after detecting the coincidence at comparing part between the key part of a read-out data sent from an address converting buffer and the part corresponding to the address information set to an address register.

CONSTITUTION: In a real channel controller, a virtual machine identifier and a part of the real addresses on virtual machine among the data which are read out of an address converting buffer 2 are turned into a key part. A part of a data other than those which are turned into the address information among those data is delivered to a signal line 104. A comparing part 4 compares the data of the key part which is fed from an address register 1 via a signal line 100 with the key part which is fed from the buffer 2 via the line 104. Then the state of the signal of a signal line 108 is set at "1" when the coincidence is obtained between the corresponding parts of information. A selecting part 4 selects a data part on the contents of the buffer 2 which are fed to a signal line 105. This data part is turned into a part of the real address on a signal line 107. Thus an address is converted at a high speed for a virtual machine system.