The present invention provides a highly-sensitive thermal-type flow-rate sensor with enhanced reliability. Provided is a thermal-type flow-rate sensor including: a passage into which a measurement-target fluid is introduced; and a sensor element (1) which is provided in the passage (21) and which measures the flow rate of the measurement-target fluid. The sensor element (1) includes: a semiconductor substrate (2); a hollow portion (29) formed in the semiconductor substrate (2); and a heating resistor (5) formed on an electric insulating film (3a, 3b) above the hollow portion (29). The sensor element (1) measures the flow rate of the measurement-target fluid by radiating heat from the heating resistor (5) to the measurement-target fluid. When Lh is the length of the heating resistor (5) in a direction perpendicular to a flowing direction of the measurement-target fluid and Wd is the shortest distance to an upstream-side edge of the heating resistor (5) from an edge of the hollow portion (an outer peripheral edge of a diaphragm) in the flowing direction of the measurement-target fluid, Wd ‰¥ 0.4 × Lh is satisfied in a relation between Lh and Wd.
