The present disclosure has an object of proposing a method and a device for estimating the state of a transmission path or an optical transmitter capable of mechanically estimating a factor causing an error with a small amount of constellation data and a low computing amount. The present disclosure provides a device for estimating a state of optical communication, the device including: a data preprocessing unit that reduces the number of data using random sampling with respect to constellation data in which an amplitude and a phase of optical communication data are represented by a polar coordinate diagram and performs distribution calculation and a dimension reduction; a learning unit that learns a dictionary matrix in sparse coding using learning constellation data processed by the data preprocessing unit; and a recognition unit that calculates a sparse coefficient using recognition constellation data processed by the data preprocessing unit and the dictionary matrix learned by the learning unit and estimates a factor causing degradation of the optical communication using the calculated sparse coefficient.