An IO adapter for guaranteeing the data transfer bandwidth on each capsule interface when multiple capsule interfaces jointly share the DMA engine of the IO adapter. An IO driver containing a capsule interface information table including bandwidth information and for setting the forming status of a pair of capsule interfaces and, during data transfer subdivides the descriptors for the capsule interfaces into multiple groups for each data buffer size satisfying the preset bandwidth information and, copies one group at each fixed sample time set by the descriptor registration means, into the descriptor ring and performs DMA transfer. To control this copy information, the IO driver contains a ring scheduler information table for managing the number of descriptor entries for the capsule interface cycle time and, a ring scheduler cancel means for renewing the entries in the ring scheduler information table each time one transmission of the descriptor group ends.