A signal processing method for a Coriolis flowmeter in which at least one flow tube or a pair of flow tubes (2, 3) which is included in a measurement flow tube is operated by a driving device using a vibrator to alternately drive the at least one flow tube or the pair of flow tubes (2, 3), and a vibration frequency of the at least one flow tube or a pair of flow tubes (2, 3) is detected by vibration detection sensors (7, 8) which are composed of a pair of velocity sensors or a pair of acceleration sensors when the at least one flow tube or the pair of flow tubes (2, 3) is vibrated, and a phase difference proportional to a Coriolis force acting on the at least one flow tube or the pair of flow tubes (2, 3) is detected to thereby obtain a mass flow rate of a fluid to be measured, the signal processing method being characterized by comprising: - converting an analog flow rate signal of a first vibration detection sensor into a first digital signal by a first A / D converter, - converting an analog flow rate signal of a second vibration detection sensor into a second digital signal by a second A / D converter, - measuring a measurement frequency value θ of said first or second digital signal and being adapted to output said frequency measurement value θ to a transmitter by a frequency measurement unit, - determining an output frequency value θXn corresponding to a difference between a set frequency value θC and said measurement frequency value θ and being adapted to output said output frequency value θXn as a control or reference signal based on the measured frequency to first and second frequency conversion sections (110, 140) by said transmitter, - moving the frequency of said first and second digital signals to another frequency band by shifting the frequency of said first and second digital signals using said output frequency value θXn, thereby obtaining first and second frequency shifted digital signals by said first and second frequency conversion sections (110, 140), - measuring a phase difference between said first and second frequency shifted digital signals by a phase difference measurement section. - converting an analog flow rate signal of a first vibration detection sensor into a first digital signal by a first A / D converter, - converting an analog flow rate signal of a second vibration detection sensor into a second digital signal by a second A / D converter, - measuring a measurement frequency value θ of said first or second digital signal and being adapted to output said frequency measurement value θ to a transmitter by a frequency measurement unit, - determining an output frequency value θXn corresponding to a difference between a set frequency value θC and said measurement frequency value θ and being adapted to output said output frequency value θXn as a control or reference signal based on the measured frequency to first and second frequency conversion sections (110, 140) by said transmitter, - moving the frequency of said first and second digital signals to another frequency band by shifting the frequency of said first and second digital signals using said output frequency value θXn, thereby obtaining first and second frequency shifted digital signals by said first and second frequency conversion sections (110, 140), - measuring a phase difference between said first and second frequency shifted digital signals by a phase difference measurement section.