A detector detects an exciting force externally exerted on a vibrating gyroscope by measuring a cross vibration of a regular triangular prism-shaped vibrating body having piezoelectric elements. The detector comprises an oscillator for oscillating the vibrating body at a constant frequency, a differential amplifier for differentially amplifying the piezoelectric voltages from two of the piezoelectric elements, a rectifier for rectifying an alternating current signal from the differential amplifier based on the oscillating phase of the oscillator, a direct current amplifier for amplifying a direct current signal from the rectifier, a controller for controlling output from the direct current amplifier, two operators for operating the oscillating signals from the oscillator with the signals supplied from the controller, and switches for switching on and off the output-lines of the two operators so that the piezoelectric signal supplied to the amplifier becomes a periodic linear signal.