An adjustable hinge device is provided for a foldable apparatus in accordance with the present invention. The foldable apparatus, such as a portable mobile phone, comprises a cover and a body connected by the hinge so as to make the cover rotatable relative to the body between a fully opened position and a fully closed position. When the cover rotates to the fully opened position, a maximum opening angle is defined. According to the relative movement between a rotatable portion and a fixed portion of the adjustable hinge, the maximum opening angle can be adjusted to fit different requirements.