An assembling device is disclosed. The assembling device is used to assemble a plastic frame and a back plate together and includes: a pressing mechanism configured to press a region of the plastic frame; and a supporting device. The supporting device includes: a supporting platform configured to support the back plate and the plastic frame; and a supporting frame configured to support the pressing mechanism. The pressing mechanism is configured to contact the plastic frame at least one contact point, and a direction of a resultant force of forces applied at the at least one contact point by the pressing mechanism is at an acute angle with respect to a plane where a top surface of the plastic frame lies.