In a method of monitoring processing load, every time a computer device executes each of a plurality of processes, for the interrupt of each of which a priority level is specified in advance, the computer device is caused to measure an index representing the processing load of each process, store the latest measurement value for each priority level, and update the maximum value with the latest measurement value when the latest measurement value exceeds the maximum value measured thus far. Further, with the reception from a host controller of a measurement result transmission request requesting transmission of the latest measurement value as a trigger, the computer device transmits the latest measurement value and maximum value at that time to the host controller, and the host controller stores the latest measurement value and maximum value transmitted from the computer device in a storage device.