An image signal processing apparatus includes a first control unit starting activation in response to an activation request, a decoding unit, and a second control unit. Each of the decoding unit and the second control unit starts activation when the first control unit completes the activation, and shifts from an off-state to a normal operating state after the activation is completed. In the normal operating state, the decoding unit receives an image signal from outside and outputs the image signal after executing a decoding process to the image signal. In the normal operating state, the second control unit processes an image included in the image signal outputted from the decoding unit, and displays the processed image. When the first control unit completes the activation and the decoding unit completes the activation, the first control unit instructs the decoding unit to perform a setting for executing the decoding process.