A combustion oscillation estimating apparatus (100, 100', 100") which estimates combustion oscillation in a combustion chamber (10, 10') connected with a burner (20, 20a, 20b) so that a flame (30, 30a, 30b) is injected by the burner (20, 20a, 20b), comprising: an input unit (110, 110") which is adapted to receive data comprising an inlet pressure (P 0) of the burner (20, 20a, 20b); and a control unit (120, 120") adapted to calculate a pressure (P 1) in the combustion chamber (10, 10') based on the inlet pressure of the burner, a shape from the burner (20, 20a, 20b) to the combustion chamber (10, 10'), a temperature distribution in the combustion chamber (10, 10'), and a shape of the flame (30, 30a, 30b), and then to estimate a status of amplitude of combustion oscillation frequencies and instability in the combustion chamber, characterized in that the control unit (120, 120") is adapted to calculate the pressure (P 1) in the combustion chamber (10, 10') using a transfer matrix having an eigenvalue calculated based on one of shape-related data from the burner (20, 20a, 20b) to the combustion chamber (10, 10'), temperature distribution-related data in the combustion chamber (10, 10'), and shape-related data of the flame (30, 30a, 30b); wherein the shape-related data from the burner (20, 20a, 20b) to the combustion chamber (10, 10') comprises at least one of shape-related data of the burner (20, 20a, 20b), shape change-related data of a connection portion between the burner (20, 20a, 20b) and the combustion chamber (10, 10'), and shape-related data of the combustion chamber (10, 10'); and wherein the control unit (120, 120") is adapted to calculate the pressure (P 1) in the combustion chamber using a global matrix (T OP) made by summing a burner shape transfer matrix (T B) based on the shape-related data of the burner (20, 20a, 20b), a shape change transfer matrix based (T A) on the shape change-related data of the connection portion between the burner (20, 20a, 20b) and the combustion chamber (10, 10'), a combustion chamber shape transfer matrix (T F) based on the shape-related data of the combustion chamber (10, 10'), a temperature distribution transfer matrix (T FR) based on the temperature distribution-related data in the combustion chamber (10, 10'), and a flame shape transfer matrix (T FM) based on the shape-related data of the flame (30, 30a, 30b). an input unit (110, 110") which is adapted to receive data comprising an inlet pressure (P 0) of the burner (20, 20a, 20b); and a control unit (120, 120") adapted to calculate a pressure (P 1) in the combustion chamber (10, 10') based on the inlet pressure of the burner, a shape from the burner (20, 20a, 20b) to the combustion chamber (10, 10'), a temperature distribution in the combustion chamber (10, 10'), and a shape of the flame (30, 30a, 30b), and then to estimate a status of amplitude of combustion oscillation frequencies and instability in the combustion chamber, characterized in that the control unit (120, 120") is adapted to calculate the pressure (P 1) in the combustion chamber (10, 10') using a transfer matrix having an eigenvalue calculated based on one of shape-related data from the burner (20, 20a, 20b) to the combustion chamber (10, 10'), temperature distribution-related data in the combustion chamber (10, 10'), and shape-related data of the flame (30, 30a, 30b); wherein the shape-related data from the burner (20, 20a, 20b) to the combustion chamber (10, 10') comprises at least one of shape-related data of the burner (20, 20a, 20b), shape change-related data of a connection portion between the burner (20, 20a, 20b) and the combustion chamber (10, 10'), and shape-related data of the combustion chamber (10, 10'); and wherein the control unit (120, 120") is adapted to calculate the pressure (P 1) in the combustion chamber using a global matrix (T OP) made by summing a burner shape transfer matrix (T B) based on the shape-related data of the burner (20, 20a, 20b), a shape change transfer matrix based (T A) on the shape change-related data of the connection portion between the burner (20, 20a, 20b) and the combustion chamber (10, 10'), a combustion chamber shape transfer matrix (T F) based on the shape-related data of the combustion chamber (10, 10'), a temperature distribution transfer matrix (T FR) based on the temperature distribution-related data in the combustion chamber (10, 10'), and a flame shape transfer matrix (T FM) based on the shape-related data of the flame (30, 30a, 30b).