Feature extraction device and state estimation system

A feature extraction device is a device that extracts a feature quantity to be input to a state estimation model for estimating a state related to a terminal where the activity is executed or a user of the terminal, which includes an acquisition unit that acquires activity history information indicating an execution history of the activity in a specified period of time and including time-series activity logs, an extraction unit that extracts co-occurrence relationship information indicating a co-occurrence relationship of activities in a specified period of time based on the activity history information, a generation unit that aggregates activity feature quantities indicating a feature of each activity based on the co-occurrence relationship information and generates an activity history feature quantity indicating a feature of the activity history information, and an output unit that outputs the activity history feature quantity as a feature quantity to be input to the state estimation model.