A concealed door closer includes a housing, an input shaft and an output shaft, the input shaft being connected to a motor, wherein a joining member is arranged between the input shaft and the output shaft, and two ends of the joining member are respectively provided with an upper connection piece and a lower connection piece, which are connected to a roller via vertical rotation shaft, and wherein both the input shaft and the output shaft are provided with a left connection piece and a right connection piece, which are horizontally connected to the roller via a horizontal rotation shaft. The components in the door closer have a simple structure and may be easily processed and assembled. The size of the joint after assembly is equivalent to that of the joining member, so the overall size is small.