A reading device for an electronic document and an operation method of reading an electronic document are provided. The reading device for the electronic document includes an input module and a main body. When the user operates the input module to move in 3D space, the input module can detect a motion state of the input module in the 3D space and generate motion data. Additionally, the main body includes a screen used for displaying a picture of the electronic document. The main body may be connected with the input module via a wireless transmission path. As a result, the main body can receive the motion data generated by the input module and compute the motion data to generate an operation instruction, and then the main body may adjust the picture of the electronic document according to the operation instruction.