INUNDATION DETECTION DEVICE, INUNDATION DETECTION SYSTEM, AND INUNDATION DETECTION METHOD

To provide a flood detection technique with which a breakdown is less likely to occur over a long period, maintenance costs are low, and the occurrence of an abnormal water level is less likely to be erroneously determined. An inundation detection device 1 detects a received signal strength I(t) that is the strength of a received response signal received from an RF sensor installed at a flood detection location, detects a dispersion D(I;[t - Δt1, t]), within a specific time Δt1, of I(t), detects a normal reception rate R[(t - Δt2, t]), and outputs a flood detection signal in a case where the dispersion D(I;[t - Δt1, t]) is greater than or equal to a specific threshold Dth1 and the normal reception rate R[(t - Δt2, t]) is less than or equal to a specific threshold Rth1. When an increase in the dispersion D(I;[t - Δt1, t]) and a decrease in the normal reception rate R[(t - Δt2, t]) are appropriately determined on the basis of the thresholds, the RF sensor that is flooded can be detected with high accuracy.