To provide the calibration method of a level sensor, enabling easy and rapidid correction of the calibration of the level sensor.

A float (14) of the level sensor (12) is lowered to the lower end (24) of an empty tank (10). The present position of the float (14) is maintained as the lowest liquid level in the electronic equipment of the level sensor (12). The empty tank (10) is turned over with the level sensor (12) so as to array the upper end (28) of the tank to the lower end, and the lower end (24) of the tank to the upper end. With the empty tank (10) at this position, since the float (14) is lowered down to this position of the upper end (28) of the tank, the float (14) is maintained at this position as the highest liquid level in the electronic equipment for the sensor of the level sensor (12).