An engine sound processing system (1, 101, 201, 301) comprising: a microphone (10, 110, 120) which is disposed outside a vehicle cabin of an automobile and which picks up an engine sound of the automobile; a sensor (30, 130, 131, 132) for detecting driving condition of the automobile; a signal processing section (2, 102) which processes the engine sound picked up by the microphone in accordance with the detected result by the sensor and outputs a processed engine sound, wherein the signal processing section includes a filter (114, 124) which exhibits a sound-insulation characteristic for simulating a sound insulation characteristic of a wall surface of the vehicle cabin and processes the the engine sound picked up by the microphone; characterized by: a control section (3, 103) which determines a signal processing characteristic according to the detected result by the sensor and which controls the signal processing section according to the determined signal processing characteristic, whereby the signal processing section further comprises: frequency analysis means (115, 125) for analyzing a frequency of the engine sound to determine a spectrum of the engine sound; and a conversion section (116, 126) which transforms the spectrum of the engine sound according to the determined signal processing characteristic and in that the signal processing section outputs the processed engine sound in which the spectrum of the engine sound is transformed. a microphone (10, 110, 120) which is disposed outside a vehicle cabin of an automobile and which picks up an engine sound of the automobile; a sensor (30, 130, 131, 132) for detecting driving condition of the automobile; a signal processing section (2, 102) which processes the engine sound picked up by the microphone in accordance with the detected result by the sensor and outputs a processed engine sound, wherein the signal processing section includes a filter (114, 124) which exhibits a sound-insulation characteristic for simulating a sound insulation characteristic of a wall surface of the vehicle cabin and processes the the engine sound picked up by the microphone; characterized by: a control section (3, 103) which determines a signal processing characteristic according to the detected result by the sensor and which controls the signal processing section according to the determined signal processing characteristic, whereby the signal processing section further comprises: frequency analysis means (115, 125) for analyzing a frequency of the engine sound to determine a spectrum of the engine sound; and a conversion section (116, 126) which transforms the spectrum of the engine sound according to the determined signal processing characteristic and in that the signal processing section outputs the processed engine sound in which the spectrum of the engine sound is transformed. a control section (3, 103) which determines a signal processing characteristic according to the detected result by the sensor and which controls the signal processing section according to the determined signal processing characteristic, whereby the signal processing section further comprises: frequency analysis means (115, 125) for analyzing a frequency of the engine sound to determine a spectrum of the engine sound; and a conversion section (116, 126) which transforms the spectrum of the engine sound according to the determined signal processing characteristic and in that the signal processing section outputs the processed engine sound in which the spectrum of the engine sound is transformed. frequency analysis means (115, 125) for analyzing a frequency of the engine sound to determine a spectrum of the engine sound; and a conversion section (116, 126) which transforms the spectrum of the engine sound according to the determined signal processing characteristic and in that the signal processing section outputs the processed engine sound in which the spectrum of the engine sound is transformed.