PURPOSE: To obtain a filter circuit for an electromagnetic pickup, whose S/N ratio is not deteriorated even if the frequency of a low-frequency noise is increased together with a detected rotation signal, and which can generate the filter output signal high in resolution all the time.

CONSTITUTION: A high-pass filter 3 is constituted of a plurality of circuit elements 32-34, which are connected in parallel one another, and switching means SW1 and SW2, which are connected to at least one of the circuit elements in series and are opened and closed in response to the voltage value of the detected rotation signal Vi. The cutoff frequency of the high-pass filter is switched so that the cutoff frequency is increased in response to the increase in voltage value of the detected rotation signal.