To provide a pulse width shaping circuit for converter use and a vortex flowmeter contributing to the prevention of false counting (false output).

The pulse width shaping circuit for converter use 6 is provided between a waveform shaping device 4 and a false output prevention device 5 between a flow detection section 1 and a flow counting mechanism 3. The pulse width shaping circuit for converter use 6, when pulse signals with high frequency of a predetermine value or more are consecutively input, couples these high-frequency pulse signals to convert them into a low-frequency pulse signal and then outputs them to the false output prevention device 5 having a low-cut function. The vortex flowmeter is constructed by a converter 2 including the pulse width shaping circuit for converter use 6.

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