An excrement property estimation model learning device includes a training data acquisition unit configured to acquire training data including input-side training data including an excrement space which is a predetermined space where there is excrement from an animal being reared, and learning image data that is image data of a captured image obtained by capturing the excrement space, and a correct label indicating whether any abnormal excrement that is abnormal excrement is reflected in an image shown in the learning image data, an excrement property estimation learning model execution unit configured to use an excrement property estimation learning model, which is a machine learning model for estimating a probability that abnormal excrement is reflected in the learning image data, to estimate the probability that abnormal excrement is reflected in the image shown in the learning image data, and an update unit configured to update, on the basis of a difference between an estimation result from the excrement property estimation learning model execution unit and the correct label, the excrement property estimation learning model such that the difference is reduced.