Magnetic disk apparatus with lower probability of occurrence of read errors due to scratch or the like on magnetic disk surface

A magnetic disk apparatus comprising:

• a head for reading recorded information from a disk provided with a servo field and a SYNC area, and a data area following said servo field;
• a gate for applying a signal read by said head to a signal processing unit;
• and
• a control unit for controlling said gate;
• wherein said control unit carries out control such that said gate is opened after an elapse of a set period of time (T1) as measured from a moment in time at which a reference signal (STM2) in said servo field has been detected from the signal read by said head, and
• wherein, if said reference signal (STM2) has not been detected after an elapse of a predetermined period of time (T) following the detection of a preceding reference signal (STM1), said predetermined time (T) corresponding to a period of time within which reference signal (STM2) should have been detected, then said gate is opened after elapse of a period of time corresponding to said predetermined period of time (T) and said set period of time (T1), as measured from a moment in time at which said preceding reference signal (STM1) was detected.