The present invention relates to a portable mosquito repelling device, wherein an ultrasonic wave oscillating device is forwardly and backwardly vibrated in an accommodating unit so that ultrasonic waves can be maximally amplified by means of resonance. Conventional portable mosquito repelling devices are produced in a small size to have an ultrasonic wave oscillating device having a small capacity, so that there are limits in repelling mosquitoes. To solve this problem, in the present invention, an operating button and an ultrasonic wave discharging hole are formed on the front surface of a housing. The operating button generates ultrasonic waves from a power source supplied from a battery equipped therein, and the ultrasonic wave discharging hole discharges the generated ultrasonic waves to the outside. An ultrasonic wave oscillating device is equipped in the housing. A cover is coupled with the rear surface of the housing, and the cover includes a fixing unit and a fixing clip. The fixing unit is downwardly pressed by a user so that the cover is opened and the battery can be replaced, and the bottom of the fixing clip is adhered on the surface of the cover by means of elasticity. In the housing, an accommodating unit is formed in a position corresponding to the ultrasonic wave discharging hole. The ultrasonic wave oscillating device is inserted in the accommodating unit and is sealed by means of an accommodating unit cover so that ultrasonic waves can be amplified and diffused by means of resonance. Openings are respectively formed in the accommodating unit and the accommodating unit cover so that a wire connecting a PCB and the ultrasonic wave oscillating device can pass therethrough. Accordingly, in the present invention, the ultrasonic wave oscillating device is inserted in the accommodating unit formed in the housing to be forwardly and backwardly vibrated without flowing left and right. Ultrasonic waves are amplified and diffused by means of resonance in the
