In order to calculate a threshold value for a detection signal output from an optical sensor in accordance with a state of a target object in a liquid ejecting apparatus, the optical sensor includes a light emitting element operable to irradiate the detected object and a light receiving element operable to detect a light amount which varies in accordance with the state of the target object. The detection signal is output from the optical sensor, based on the detected light amount. A level of the detection signal is adjusted so as to fall within a prescribed range. The threshold value is calculated based on the adjusted level of the detection signal.