Position controller and controlling method, optical disc recorder and recording method and optical disc reproducer and reproducing method

A position control apparatus which includes position error signal detection means for detecting a position error signal of the mechanical part and position control means for controlling the position of the mechanical part by supplying to it the position error signal from the position error signal detection means, whereby the apparatus has provided therein phase compensation means comprising a digital filter; the position error signal is supplied to the phase compensation means to perform phase compensation thereon and the phase-compensated position error signal is supplied to the position control means; and, when starting a closed-loop control, filter variables that were used at a time preceding by an amount of time equal to or greater than that corresponding to the amount of one sampling time of the digital filter have been reset.