A changing device includes a feed component, a winder, a desizing oven, a coating component and a sizing component, and the feed component is provided for supplying a carbon fiber material, and a thermosetting resin oil is covered onto a surface of the carbon fiber material, and a desizing oven is provided for removing the thermosetting resin oil form the surface of the carbon fiber material, and then the coating component coats a surfactant onto the surface of the carbon fiber material, and finally the sizing component is used to coat a thermoplastic resin oil onto a surface of the surfactant to form a carbon fiber product to be wound onto a rewinding part of the winder, so as to produce a carbon fiber product with a thermoplastic resin oil coated onto a surface of the carbon fiber product.