A weighing apparatus has a weighing conveyor with a conveyor belt driven by a drive motor for transporting and weighing an object at the same time and outputting a weight signal indicative of its weight. The lengths of the weighing conveyor and the object in the direction of transportation are inputted and the weight signals outputted by the weighing conveyor are filtered so as to eliminate vibration components due to the vibration of the conveyor. The distance traveled by the object on the weighing conveyor is detected from the angle of rotation of the drive motor, and the timing for processing the weight signals, or when to start the measurement of weight and when to obtain the weight value, is determined independent of the transportation speed of the belt but from the detected distance traveled by the object and the inputted length values.