A hydrodynamic bearing having a bearing sleeve, a rotational shaft supported for rotation by the bearing sleeve, a bearing gap formed between the bearing sleeve and the rotational shaft, lubricating oil contained within the bearing gap, at least one hydrodynamic pressure-generating groove formed at an inner peripheral surface of the bearing sleeve; and an oil reservoir. When the new music content is to be used, a search is made for original music content on the basis of information identifying a replicated-from source and use of the new music content is permitted only when the c original music content has been successfully found. The method of the invention groups a plurality of signals according to the magnitude of signals, and sequentially performs interference cancellation with respect to the groups in order of the signal magnitude. The actuator displaces the second portion with respect to the first portion, and the controller operates the actuator and determines displacement of the second portion with respect to the first portion.