A learning diagnostic system for a working machine that includes a machine body mounted with a working implement, the learning diagnostic system detecting a state quantity of the working machine with a sensor (34, 35) and inputting the data as running data to thereby detect a fault in an operating state of the working machine using the running data, characterized in that the system comprises: a state learning device for sorting the inputted running data into running data when the operating state of the working machine is a steady operating state and running data when the operating state of the working machine is a transient operating state, learning the operating state of the working machine based on the sorted running data, and generating steady state information and transient state information, each including a permissible error; and a state diagnostic device for determining, using the inputted running data and the steady state information including the permissible error and generated in the state learning device, whether the operating state of the working machine related to the inputted running data is the steady operating state or the transient operating state, making a fault determination in the determined steady operating state, and using the transient state information including the permissible error and generated in the state learning device to make a fault determination in the determined transient operating state, wherein: the state learning device selects, of the running data when the operating state is the transient operating state, running data in an interval continuous with respect to time; selects, of the running data when the operating state is the steady operating state, running data in two steady operating states before and after transition to the transient operating state in which the running data is selected; and generates the transient state information based on the running data selected in the two steady operating states and the running data selected in the transient operating state; and the state diagnostic device searches through the transient state information generated in the state learning device based on the two steady operating states before and after the transition to the determined transient operating state to thereby extract corresponding transient state information, and makes a fault determination in the determined transient operating state based on the determined transient operating state and the extracted transient state information. a state learning device for sorting the inputted running data into running data when the operating state of the working machine is a steady operating state and running data when the operating state of the working machine is a transient operating state, learning the operating state of the working machine based on the sorted running data, and generating steady state information and transient state information, each including a permissible error; and a state diagnostic device for determining, using the inputted running data and the steady state information including the permissible error and generated in the state learning device, whether the operating state of the working machine related to the inputted running data is the steady operating state or the transient operating state, making a fault determination in the determined steady operating state, and using the transient state information including the permissible error and generated in the state learning device to make a fault determination in the determined transient operating state, wherein: the state learning device selects, of the running data when the operating state is the transient operating state, running data in an interval continuous with respect to time; selects, of the running data when the operating state is the steady operating state, running data in two steady operating states before and after transition to the transient operating state in which the running data is selected; and generates the transient state information based on the running data selected in the two steady operating states and the running data selected in the transient operating state; and the state diagnostic device searches through the transient state information generated in the state learning device based on the two steady operating states before and after the transition to the determined transient operating state to thereby extract corresponding transient state information, and makes a fault determination in the determined transient operating state based on the determined transient operating state and the extracted transient state information.