A portable electronic device comprises a cover member, a body member, and a power generating assembly. The cover member is slidably mounted to the body member. The power generating assembly includes a power generating device and a rack assembly. The power generating device includes a toothed gear and a stator. The toothed gear is rotatably clockwise or counter clockwise mounted to the stator. The stator is fixed to the body member. The rack assembly includes a fastening portion and a rack portion opposite to the fastening portion. The fastening portion is fixed to the cover member. The rack portion meshes with the toothed gear, thus the power generating device driving the rack assembly and the cover member to slide relative to the body member.