PURPOSE: To measure a disc to be measured within a short time without moving said disc from a measuring environment, by measuring off-track amounts at a plurality of points on one round of a track under environments different in temp. or humidity and calculating the difference thereof to perform operation processing.

CONSTITUTION: After the signal of a disc 1 to be measured is regenerated and amplified by an amplifier 3, the amplified signal is subjected to DC conversion by an AC-AD converter circuit 4 while reacted only with a label mark recorded so as to be differentiated from a burst data block in recording frequency by a label mark detection circuit 5 to generate a pulse signal. When the measuring switch of an input apparatus 8 is pushed, an A/D conversion starting signal is sent to an A/D converter 6 and this A/D converter 6 converts the pulse output signal of the label mark detection circuit 5 to a trigger signal to continuously sample the output of the converter circuit 4 during one rotation of the disc 1 and data is transmitted to a microcomputer system apparatus 7 and operation is performed on the basis of this data to measure an off-track amount.