A pressure sensitive adhesive sheet is provided which comprises a pressure sensitive adhesive layer formed of a pressure sensitive adhesive composition. The pressure sensitive adhesive composition contains an aliphatic polycarbonate and a pressure sensitive adhesive resin other than the aliphatic polycarbonate. The pressure sensitive adhesive sheet can be reduced in the adhesive strength at desired timing by a novel mechanism of action so that the release of an adherend becomes easy. The above pressure sensitive adhesive composition preferably contains an acid/base generator that generates an acid or a base by applying energy.