To provide a method for constantly adjusting and observing the flow rate of gas containing moisture for each branch by largely dividing a throwing gas path into degreasing, burning, reoxidation, and the like so that the constituent of gas containing moisture in the furnace forms a specific concentration distribution along a direction for carrying an object to be treated and further providing a proper number of branches for each zone in a tunnel type continuous moisture-containing gas atmosphere burning furnace.

A piece of moisture-containing equipment is provided to each zone of degreasing, burning, reoxidation, and the like along the direction of transport in the furnace for supplying a specific gas constituent containing moisture to each zone, and further a required number of branches are provided to each zone, a flowmeter for constantly setting and observing the flow rate of gas containing moisture can be fitted to each branch, and a specific amount of gas containing moisture is dispersed and thrown into a plurality of locations in the furnace, thus making uniform the concentration of the gas constituent containing moisture in each zone, or forming a specific concentration distribution, and hence easily achieving desirable atmospheric conditions in terms of quality of the object to be treated. Also, as the flowmeter that is constantly capable of setting and observing the flow rate of the gas containing moisture, the flowmeter is provided with countermeasures against dew formation where, for example, a heater for increasing temperature, a temperature detection means, and a temperature control means are combined.