A plant monitoring apparatus 100 includes: a soil state estimation unit 200 that estimates a state of soil by, with use of frequency association information calculated based on vibration measured via the soil, referencing soil state estimation information in which the frequency association information and information indicating states of the soil are associated with soil states; and a plant state estimation unit 300 that estimates a state of a plant by, with use of growth association information that was calculated based on vibration of the plant and indicates growth of the plant, referencing plant state estimation information in which the growth association information and information indicating states of the plant above a plant soil surface are associated with plant states above the plant soil surface.