At least one processor included in an optical signal state estimation apparatus carries out: an acquisition process for acquiring a constellation of an optical signal; a generation process for generating time series data in which pieces of histogram information are arranged in time series, the histogram information being obtained by counting the number of signal points of the constellation, the signal points being included in each of grids obtained by dividing an in-phase component direction and a quadrature component direction into a specific number of rows and the specific number of columns, respectively; and an estimation process for estimating a state of the optical signal by inputting the time series data to a learned model.