PURPOSE: To obtain a pumping loss reduction effect in an operation region of wide range, by variably setting an opening position of a communication path which connects a pair of working chambers neighboring to each other interposing an intermediate housing.

CONSTITUTION: Of the respective working chambers contained in a pair of trochoid spaces 15, 16 neighboring to each other interposing an intermediate housing 6, a working chamber 16A is in a compression stroke of the one trochoid space 16 while a working chamber 15A is in an intake stroke of the other trochoid space 15, and a communication path 30, in which the working chambers 16A and 15A communicate with each other, is provided. And a rotary valve 40, which is mounted so as to traverse each port 31, 32, 33 of the communication path 30, closes all the ports 31, 32, 33 in a high load operation region while respectively alternatively opens only the third port 33 of the earliest close timing in an intermediate load operation region and only the second port 32 in a light load operation region further only the first port 31 of the latest close timing in a very light load operation region.