The present invention provides a high frequency amplifier suitable for use in a wireless communication system which performs detection of an output level necessary for feedback control by a current detection system, wherein control sensitivity in an area low in transmit request level is lowered so that an output level can be controlled over the whole control range with satisfactory accuracy. A notification terminal device, a plurality of printers serving as the network terminal devices, a plurality of personal computers serving as the notifying terminal devices, and the like are connected to the network. The method also includes decoding the bit stream in the picture layer using the extension data of an anterior header of the picture layer when an extension start code indicating the beginning of the extension data of the current header is not received from the bit stream.