To open a folding type cellular phone in a single operation by one hand.

In the device opening the folding type cellular phone 2, a device body 4 is provided from an installing potion 3 installed to the cellular phone. The device so as to protrude body 4 has an arm 5 capable of rotating between opening/closing positions of a cover, and a pressing piece 6 arranged between a grip and the cover of the cellular phone is provided at the tip of the arm. The arm is energized by a spring so as to push up the cover of the cellular phone in an opening direction by the pressing piece. The device body is provided with a holding mechanism holding the arm at a closing position against the spring, and an operable holding releasing means 8 releasing the holding by the holding mechanism and rotating the arm to an angle at which a push-up force by the spring is effected.