Thermal Flow Meter

A thermal flow meter having a bypass passage for flowing measurement target gas which is taken from a main passage, and an air flow sensing portion for measuring a flow rate of the measurement target gas by carrying out heat transfer in relation to the measurement target gas which flows in the bypass passage, comprising:

• a circuit package which has the air flow sensing portion and is formed by a first resin;
• a resin housing which forms a bypass passage trench constructing a part of the bypass passage and is formed by a second resin so as to fix the circuit package;
• and
• a resin cover which forms the bypass passage by covering the bypass passage trench,
• wherein an end face of a bypass passage forming wall forming the bypass passage of the housing and a rear face of the cover are welded by the laser,
• wherein a concave trench is formed along the weld portion at a position which is closer to the bypass passage than the weld portion of the housing welded to the cover, and
• wherein the concave trench is formed in such a manner that a part of an interface between the bypass passage forming wall including the weld portion and the cover is positioned in a wall surface of the concave trench.