crank shaft 16 which is rotated by the engine 12 the drive member 15 is provided at an inner side thereof with a plurality of circumferentially equi space projections 17 each of which extends inwardly in the radial direction an inner end portion of each projection 17 is in sliding engagement with an outer surface of a hub 18 which is fixedly mounted on the cam shaft 11 and is enclosed by the drive member 15 between the drive member 15 and the hub 18 there are defined six chambers 20 21 22 23 24 and 25 which are arranged in an equi spaced manner in the circumferential direction each chamber 20 21 22 23 24 and 25 has a pair of circumferentially opposed radially extending walls 20a and 20b 21a and 21b 22a and 22b 23a and 23b 24a and 24b 25a and 25b on the hub 18 six vanes 30 31 32 33 34 and 35 are fixedly mounted in an equi spaced manner in the circumferential direction the vane 30 which projects outwardly from the hub 19 in the radial direction is extended into the corresponding chamber 20 so that the chamber 20 is divided into a first section 20c and a second section 20d both of which are fluid tightly separated from each other the chambers 21 22 23 24 and 25 are so divided in a manner similar to the chamber 20 in the condition shown in fig2 the vanes 30 31 32 33 34 and 35 are in abutment with the walls 20a 21a 22a 23a 24a and 25a respectively for maintaining such a condition a first connecting means 36 is employed the connecting.