Provided are a pen state detection circuit, a pen state detection system, and a pen state detection method that can improve estimation accuracy for a pen state in an electronic pen including at least one electrode. A pen state detection circuit acquires, from a touch sensor, a first signal distribution indicating a change in capacitance associated with approach of a first electrode and uses a machine learning estimator to estimate an instruction position or an inclination angle of an electronic pen from first feature values related to the first signal distribution. The first feature values include first local feature values related to a first local distribution corresponding to sensor electrodes in a number fewer than the number of arranged sensor electrodes exhibiting the first signal distribution.