In the example as shown in FIG. 14, to generates L (three, in this example) pilot blocks of .lambda. bitsbefore and after the n-th pilot symbol, pilot symbols from (n-K+1)-th to (n+K)-th pilot symbol are used, where K is a natural number equal to L.times..lambda..It is preferable that the pilot blocks be formed from pilot symbols belonging to many different slots to use these pilot symbols for the