To do a greater number of operations simply without an additional troublesome pressure step controller by installing an actuation mechanism in which a pressure converter is equipped with an actuation mechanism surface which is loaded with pressure fluid stepwise in sequence.

A pressure converter 103 has the third expansion chamber 129 connected with the first pressure fluid system 107 and the third actuation mechanism surface 130 which becomes effective in the third expansion chamber 129. The first pressure fluid 106 guided into the system 107 can be supplied only to one expansion chamber selected from the first expansion chamber 105 and the third expansion chamber 129 and also can be supplied simultaneously to both chambers 105, 129. By loading the first actuation mechanism surface 104 and the second actuation mechanism surface 108 in turn or stepwise with the first pressure medium 106, an actuation mechanism 101 becomes movable stepwise. Piston cylinder units 118, 125, 218, 225 become switchable in turn or stepwise.