PURPOSE: To shorten the time required for the output characteristics to become stable against the variation in temperature of a fluid whose flow rate is measured and to prevent the output from being influenced by the ambient temperature.

CONSTITUTION: Heat conducting plates 20a, 20b, 20c and 20d made of aluminium and/or copper are stuck to the outer circumference of a frame body which has reinforcing materials 4a and 4b integrated in square form with fixing materials 3a and 3b in such a manner that the heat conducting plates 20c and 20d are in direct contact with a measuring 2. Heat of the fluid whose flow rate is to be measured is transferred quickly to the outside air thorugh the measuring pipe 2, the heat cnducting plates 20c and 20d, and the heat conducting plates 20a and 20b. As a result, the temperatures of the measuring pipe and the frame body as caused by changes in the temperature of the measuring fluid become stable at an almost equal value in a short time thereby allowing the holding axia heat stress applied to the measuring pipe 2 to be lowered. Thus, the effect of the temperature of the fluid on the output characteristics is stabilized quickly and moreover, the effect during the stabilization thereof can be checked to be at a low level.