A mobile telephone screen is covered with a lens, fixed on one end and set free on the other or fixed on both ends. When the fonts don't need to be magnified, the Fresnel lens tightly sticks to the mobile telephone screen; and when need, the free end of the Fresnel lens will be unfolded or both ends of it will be carried as a whole to magnify the fonts. Without increase in the thickness of mobile phone, the fonts on screen can be magnified conveniently and a magnification scale can be freely adjusted according to the magnitude of the unfold or the carry. A bridge piece in the device has the an adjustable and telescopic structure that can be adjusted according to the width of the mobile phone. A suction cup is elastic one that can adhere to the both sides of mobile phone.