Provided are an image signal processing apparatus and a controlling method thereof. The image signal processing apparatus includes a signal decoder, an image signal processor, a display, a controller, a memory, and a power interface. The signal decoder decodes input signals, and the image signal processor processes signals decoded by the signal decoder so that they are outputable. The display outputs the signals processed by the image signal processor, and the controller allows a list of modules recognized by the connector to be displayed, and controls driving of the module selected by a user. The memory stores a program transmitted from the selected module, and the power interface supplies power to the module.