A micromachined pump apparatus 1 includes a substrate 2 having upper and lower surfaces and a plurality of lengthwise arranged apertures 2A-2E, each of which has an upper surface opening and a lower surface opening. A plurality of diaphragms 6A-6E close the upper surface openings of the apertures 2A-2E, respectively. A guide plate 3 is fixedly mounted on the upper surface of the substrate 2 and defines a passage 3a through which an object fluid is moved by cooperating with the diaphragms on the upper surface of the substrate 2. A base plate 4 is fixedly mounted at its upper surface on the lower surface of the substrate 2, thereby enclosing an operating fluid in each of the apertures 2A-2E. An electrically operated heater device 5 is provided on the upper surface of the base plate 4 for heating the fluids in the apertures 2A-2E, respectively, in such a manner that whenever the fluids are heated the resultant expansion of the respective operating fluid expands the diaphragms, respectively, toward the passage. The expansions of the diaphragms 6A-6E are made in sequence, thereby forcing the object fluid to move through the passage 3a.