In one embodiment, a settling time determination method includes deflecting a charged particle beam by applying a voltage outputted from an amplifier to a first deflector while changing a deflection settling time, and writing an evaluation pattern, measuring a position of the evaluation pattern, and determining a position displacement amount of the measured position from a design position, performing fitting of the position displacement amount for the deflection settling time on a first output waveform of the amplifier, and determining a deflection settling time in which the position displacement amount is within a predetermined range.