Abstract: An optical calibrating apparatus includes: a laser illuminator (6) disposed in an eccentric adjusting sleeve (5), an inner inclined adjusting sleeve (4) within a jacket (3), an outer inclined adjusting sleeve (2) outside the jacket (3), and a cylindrical casing (1), in which a laser line is emitted by the illuminator (6) for checking levelling, plumbing and verticality and the laser line has been calibrated for a horizontality or a verticality by rotating the eccentric adjusting sleeve (4), the inner and outer inclined adjusting sleeves (4, 2) until the emitted laser line is aligned with a standard laser line emitted from a standard optical calibrator or aligned with a mark preset by a standard instrument.