A monitoring apparatus includes a processor configured to capture a network transmission signal from a monitoring location in a monitoring target network; specify each of a plurality of sessions based on session specifying information contained in the captured network transmission signal; analyze, for specified each of the sessions, the network transmission signal and measure a quality index; transfer the quality index of each of the sessions, which is measured every predetermined period of time, as a quality measurement result to an aggregation apparatus until a predetermined threshold value of a processing capability is reached; and stop, when the predetermined threshold value of the processing capability is exceeded, measuring the quality index of one of the sessions in a high-load state, and in a next cycle, perform the measurement on one of the sessions in the high-load state.