We report room-temperature synthesis of a covalent organic framework (COF) using the combination of benzene-1,3,5-tricarbaldehyde and 1,4-phenylenediamine. The method is quite simple and the obtained COF was revealed to have a high surface area and high thermal stability due to its high crystallinity compared to that of the COF synthesized by a conventional solvothermal synthetic method using the same monomer combination. We also synthesized a nitrogen-doped graphite based on carbonization of the COF.