Desk with changeable desk top area

A desk with changeable desk top area comprises a first main desk board, a second main desk board, a first expansion desk board, a second expansion desk board, a supporting frame and a plurality of supporting foot portions. A closing-up state and a separating state in which an assembly space is formed between the first main desk board and the second main desk board are adopted for the first main desk board and the second main desk board. The first expansion desk board and the second expansion desk board are arranged below the first main desk board and the second main desk board. The supporting frame comprises a first supporting portion, a second supporting portion, two pivoting portions and a supporting guide portion. In the closing-up state, the second expansion desk board is superposed with the first expansion desk board and abuts against the supporting guide portion, and in the separating state, the second expansion desk board is subjected to the linkage of the first expansion desk board overturning towards the first supporting portion and accordingly slides on the supporting guide portion and stops on the second supporting portion.