A working machine maintenance system having a plurality of working machines. A center server is provided that manages maintenance on the plurality of working machines by engaging in data exchange through bidirectional communication with each of the plurality of working machines via a communication line. The working machines each include an operation data storage device, an operation device operated to enter a maintenance work completion, a data transmission device, a data reception device, and a display device at which the maintenance information is displayed. The center server includes a data reception device that receives the operation data, the maintenance work completion data, and the maintenance data that have been transmitted, an operation database in which the operation data are stored, a maintenance database, a calculation device that calculates maintenance timing. and a data transmission device that transmits data related to the maintenance information.