A demodulator in a receiver has a multiple symbol differential phase detector which calculates phase differences between a received signal and received signals of 1, 2,. Upon receipt of a packet that contains an IP address in its IP header and stores a certificate in its certificate payload from a storage device 300, an authentication device 200 compares an IP address that is recorded in the certificate and the IP address that is recorded on the IP header of the packet. When a transition occurs, a counter is initiated in accordance with a second high-speed clock signal. Advantageously, continuous transitional regions are formed relative to the reshaped portions to provide vision for intermediate distances. The decrease in the number of parts and the simplification of the design allow, accordingly, an additional miniaturization.