Abstract: Provided is an environmental factor prediction device that includes a predictor and predicting means. The predictor uses, as explanatory variables: water quality data in a plurality of layers in water, the data including a value corresponding to a biochrome level or a bioluminescence level (e.g. chlorophyll concentration), water temperature, salt concentration, dissolved oxygen, turbidity and flow rate; and meteorological data including atmospheric temperature, precipitation and sunshine duration, and outputs an estimated value of each item of the explanatory variables at a unit time later, based on time series data of the explanatory variables. The predicting means predicts the water quality data up to an N unit time later by repeating prediction using the estimated value acquired by the predictor as input of the predictor again.