A posture estimation device includes: a processor that: obtains detected information indicating a feature of a subject, wherein the feature is detected based on an image that is captured by an imager from a position where the subject is viewed from above, calculates a feature amount based on the obtained detected information, updates, based on a geometric relationship between the imager and the subject, a model parameter for estimating a posture of the subject by machine learning using the calculated feature amount in a time series, and estimates the posture of the subject using the updated model parameter.
