An entertainment system comprising: a plurality of input devices in the entertainment system, wherein each input device allows a respective user to perform an input operation; a processing device which processes an application based on the inputs entered into the input devices and generates an image signal showing a processing result of the application; an image capturing device; and an image display device which outputs the image signal generated in the processing device; wherein the processing device is configured to determine if each input device is located in an image capturing space of the image capturing device based on the captured images which have been continuously captured at a predetermined capturing speed by the image capturing device, and wherein each input device has a plurality of input units (21, 27, 26) through which a user performs the input operation to make the application proceed, and a plurality of light emitting elements (40a, 40b, 40c, 40d) for expressing a number to be assigned to the input device, characterized in that: the processing device is configured to assign in the application to be executed said number to each input device participating in the application and to transmit information indicating the number assigned to each input device, each input device is configured to periodically repeat turning on and off one of the light emitting elements in a flashing pattern determined in accordance with the number assigned, wherein the flashing pattern is uniquely defined for the number assigned by having a different duty ratio of a continuous turning-on period to a continuous turning-off period, and each input device controls the turning on and off of the light emitting element with said duty ratio, and in that the processing device is configured to identify the input device holding the light emitting element based on the flashing pattern. a plurality of input devices in the entertainment system, wherein each input device allows a respective user to perform an input operation; a processing device which processes an application based on the inputs entered into the input devices and generates an image signal showing a processing result of the application; an image capturing device; and an image display device which outputs the image signal generated in the processing device; wherein the processing device is configured to determine if each input device is located in an image capturing space of the image capturing device based on the captured images which have been continuously captured at a predetermined capturing speed by the image capturing device, and wherein each input device has a plurality of input units (21, 27, 26) through which a user performs the input operation to make the application proceed, and a plurality of light emitting elements (40a, 40b, 40c, 40d) for expressing a number to be assigned to the input device, characterized in that: the processing device is configured to assign in the application to be executed said number to each input device participating in the application and to transmit information indicating the number assigned to each input device, each input device is configured to periodically repeat turning on and off one of the light emitting elements in a flashing pattern determined in accordance with the number assigned, wherein the flashing pattern is uniquely defined for the number assigned by having a different duty ratio of a continuous turning-on period to a continuous turning-off period, and each input device controls the turning on and off of the light emitting element with said duty ratio, and in that the processing device is configured to identify the input device holding the light emitting element based on the flashing pattern. the processing device is configured to assign in the application to be executed said number to each input device participating in the application and to transmit information indicating the number assigned to each input device, each input device is configured to periodically repeat turning on and off one of the light emitting elements in a flashing pattern determined in accordance with the number assigned, wherein the flashing pattern is uniquely defined for the number assigned by having a different duty ratio of a continuous turning-on period to a continuous turning-off period, and each input device controls the turning on and off of the light emitting element with said duty ratio, and in that the processing device is configured to identify the input device holding the light emitting element based on the flashing pattern.