PURPOSE: To correct writing light amount and to stabilize recording status by measuring the surface vibration and warp of an optical disc before writing.

CONSTITUTION: A carrying means 25 moves an optical pickup 5 in the diameter direction of an information recording medium 4 and the means 5, 12 detect vertical movement on the recording surface of the medium 4. Means 18W21 divide the recording surface of the medium 4 equally into M parts with a fixed pitch interval in the diameter direction and positions the means 25. The storage means 17 has a memory for M×N addresses storing N parts obtained by dividing the vertical movement of one revolution of the medium 4 equally by the means 5, 12. An arithmetic device 18 calculates the inclination of the medium in the peripheral and diameter directions from M×N address data in the means 17.