To provide a small-sized mass flowmeter having a wide measuring range.

This thermal mass flowmeter includes a planar thin substrate having a sensing face contacting directly or indirectly with a flowing fluid during measurement, and is provided, on the sensing face, with a heating means and a temperature sensor means controlled electrically for finding a temperature difference, by a planar technique. In detail, the substrate having the sensing face exists inside a cavity of a module into which a feed pipe line for the fluid and a drain pipe line come.