To prevent random access commands from remaining even in the case of mixed sequential and random accesses. A storage medium control unit is used in a data storage device adapted to perform processing on a data storage medium based on multiple requests including sequential access requests and random access requests. The storage medium control unit includes: request response delay monitoring device for monitoring the presence of delay in response to the requests based on whether or not the response time for each request exceeds a certain allowable delay time; and request control device for preventing the rearrangement processing of the sequential access requests and controlling the processing of the requests to be performed in a certain request order at the allowable delay time if exceeded.