Learning processing method for a plurality of machine tools, the method comprising the steps of: communicating, by an information processing device, with the plurality of machine tools; sensing, by a plurality of sensors (206, 207, 208) included in each of the plurality of machine tools, information about the machine tool as sensed information; receiving, by the information processing device, as collected data from each of the plurality of machine tools, part information about a part of the machine tool and the sensed information obtained by the sensors (206, 207, 208) internal to the machine tool; wherein the part information includes at least one of: a timing of replacing a part to be maintained, a part ID for identifying the part to be maintained, or an impurity level or contamination of a coolant of machine tool; storing, in a storage unit of the information processing device, the collected data received from each of the plurality of machine tools; based on the plurality of collected data stored in the storage unit, learning a normal range for sensed information by type of the part and for each of types of the plurality of sensors (206, 207, 208); receiving, by a first machine tool of the plurality of machine tools, an instruction to conduct a diagnosis; performing the diagnosis by processing a workpiece in the first machine tool and collecting sensed information by the plurality of sensors (206, 207, 208) in the first machine tool; receiving, by the information processing device, from the first machine tool, the sensed information obtained during the diagnosis; referring, by the information processing device, to a learning result obtained through the step of learning to make a diagnosis of whether each type of the sensed information received falls within a normal range corresponding thereto and thereby generating a diagnosis result; and transmitting the diagnosis result from the information processing device to the first machine tool, wherein the diagnosis result indicates whether the part needs to be replaced or not. communicating, by an information processing device, with the plurality of machine tools; sensing, by a plurality of sensors (206, 207, 208) included in each of the plurality of machine tools, information about the machine tool as sensed information; receiving, by the information processing device, as collected data from each of the plurality of machine tools, part information about a part of the machine tool and the sensed information obtained by the sensors (206, 207, 208) internal to the machine tool; wherein the part information includes at least one of: a timing of replacing a part to be maintained, a part ID for identifying the part to be maintained, or an impurity level or contamination of a coolant of machine tool; storing, in a storage unit of the information processing device, the collected data received from each of the plurality of machine tools; based on the plurality of collected data stored in the storage unit, learning a normal range for sensed information by type of the part and for each of types of the plurality of sensors (206, 207, 208); receiving, by a first machine tool of the plurality of machine tools, an instruction to conduct a diagnosis; performing the diagnosis by processing a workpiece in the first machine tool and collecting sensed information by the plurality of sensors (206, 207, 208) in the first machine tool; receiving, by the information processing device, from the first machine tool, the sensed information obtained during the diagnosis; referring, by the information processing device, to a learning result obtained through the step of learning to make a diagnosis of whether each type of the sensed information received falls within a normal range corresponding thereto and thereby generating a diagnosis result; and transmitting the diagnosis result from the information processing device to the first machine tool, wherein the diagnosis result indicates whether the part needs to be replaced or not.