PURPOSE: To prevent the occurrence of powder clogging in a flow passage in the case of a mixed flow including powder by converting a negative pressure occurring in one flow passage at or near a branch point into a positive pressure through a controlling flow, and flowing a main flow passage changing into the other flow passage.

CONSTITUTION: The one flat face of a flow passage forming body 2 is provided with an input pipe 5, a nozzle 6, the first and the second output pipes 7,8 branched by a splitter 25, the first and the second nozzles jet 9, 10, the first and the second control pipes 11,12 and flow passages for nozzles 13, 14. Vibrating body 3 made of stainless steel or ceramics thin sheet is sticked onto the above flat face of the flow passage forming body 2 except the flow passage, and a piezoelectric element to form an agitator 4 is sticked onto the vibrating body 3, and a control jet flow is rectangularly struck against a solid gaseous two-phase jet flow for converting the flow passage. Thus a fluid flow converting device can keep a long life and can be prevented from the clogging caused by mixed powder of the flow passage.