An information recording/reproducing apparatus for recording information on and/or reproducing information from a recording medium using a head. The apparatus includes a single processor and a memory device. The single processor executes data input/output processing and servo processing of a light beam from the head, while alternately switching at a predetermined period. The servo processing is divided into a plurality of blocks which are cyclically executed in turn for each predetermined period and processing required to be executed in each period is set in each block and processing not required to be executed in each period is set in only a specific block. The memory device stores contents of the processing for the respective blocks.