An oil content measurement device includes a fluid device which mixes water to be treated containing oil content with a solvent and extracts the oil content into the solvent, a sensor unit which has a casing storing a quartz crystal oscillator therein with a ring-like spacer in between, a dispensing nozzle which is disposed above the oscillator at a predetermined gap there between and feeds a predetermined amount of the solvent after the oil content has been extracted on the oscillator, a sensor circuit which measures a resonance frequency of the oscillator, and controller which controls at least the fluid device and the sensor circuit. Provided is a arithmetic logical unit, based on a change amount of the received resonance frequency of the oscillator in the sensor unit to which the solvent after the oil content has been extracted has been fed, measures the oil content remaining on the oscillator.