A disk apparatus (10) includes a spindle (62) to which a magnetooptical disk (60) is attached. An FCM is formed on the magnetooptical disk (60) along a track at intervals of a predetermined period, a laser beam having a different light amount depending on a time of an execution and an interruption of a recording process is incident upon the track. The FCM signal detection circuit (36) detects an FCM signal based on the laser beam reflected from the track, a comparator (42) compares a level of the FCM signal and a slice level, and a PLL circuit (54) generates a clock signal based on a comparison result by the comparator (42). When a change request between an execution/interruption of the recording process is applied, a predetermined first slice level is set to the comparator (42) until 200 mili seconds passes since a reception of the change request. When 200 mili seconds passes, a second slice level calculated based on a peak level of the FCM signal is set to the comparator (42).