To provide a small-scale, low-cost wave observation method and system for observing wind wave that can observe the wind wave with a long wavelength and without being affected by the change in the wind wave of an observation sea area.

A wave-observing device 10 including a GPS receiver 13 and a transponder slave station 11 is mounted to a floating target 20 for each wave observation sea area, a transponder master station 30 and a wind wave data- processing device 40 are installed on land, the transponder slave station 11 transmits each data of the latitude, longitude, and altitude of a selffloating target 20 being measured by the GPS receiver 13 to the transponder master station 30, the transponder master station 30 supplies the reception data of the floating target being received from the transponder station 11 to the wind wave data-processing device 40, and the wind wave data-processing device 40 analyzes wind wave based on the wave observation data for each wave observation sea area being supplied.