An extrusion device of a three-dimensional printer comprises a housing, a nozzle, a ratchet, an idler and a cooling mechanism. The nozzle is connected with the housing, the ratchet is disposed in the housing, and the idler is disposed adjacent to the ratchet. A thermofusible material is jointly held by the ratchet and the idler, and is guided to be extruded through the nozzle. The cooling mechanism comprises an air pump and an air pipe. The air pipe is partially disposed in the housing and connected with the air pump for guiding the air extracted by the air pump to flow into the housing through the air pipe, thereby reducing an environment temperature inside the housing. Therefore, by disposing the air-guiding cooling mechanism, the advantages of enhancing the cooling effect and the printing quality are achieved.