Disclosed herein is an apparatus for preventing an animal and method of controlling the apparatus. The apparatus includes a sound sensor for sensing a bark of an animal and converting the bark into an electrical signal. An amplifier amplifies the electrical signal. A vibration sensor senses a vibration occurring on a neck of the animal. A microprocessor performs control such that, when signals are input from the sound sensor and the vibration sensor, voice, ultrasonic or low-frequency stimulation means is output, and has an auto-variable output function and a time band-based output function. A first control switch allows the user to optionally set a type and a stimulation intensity of the stimulation means. A second control switch allows the user to optionally set a time for which the stimulation means is operated. An output unit receives control signals for the stimulation means and outputs corresponding stimulations.