A thermal type air flow meter comprising: a housing member placed in an intake passage of an internal combustion engine, wherein the intake passage constitutes a primary air passage; a base member fixed to the housing member comprising a flat plate-like board fixing part to which a circuit board is fixed, wherein said board fixing part comprises one side with a surface to which said circuit board is fixed and an opposite side with an outer surface facing away from the housing member; a secondary passage constituting part comprising a secondary passage into which part of air passing through the intake passage flows; and a flow rate detecting element placed in the secondary passage, wherein said circuit board is electrically connected to the flow rate detecting element for receiving an input of an amount of heat radiation from the flow rate detecting element, and for outputting a signal according to an air flow rate, characterized in that the base member is a resin component integrally including the board fixing part and the secondary passage constituting part providing a connection portion between the board fixing part and the secondary passage constituting part; the secondary passage constituting part constitutes the secondary passage in cooperation with the housing member; a rib (231-233, 235) is provided for improving the strength of the base member; the rib (231-233, 235) is formed integrally and protrudes from the outer surface of the board fixing part facing away from the housing member; and the rib (231-233, 235) extends along at least a part of the board fixing part to at least the connection portion. a housing member placed in an intake passage of an internal combustion engine, wherein the intake passage constitutes a primary air passage; a base member fixed to the housing member comprising a flat plate-like board fixing part to which a circuit board is fixed, wherein said board fixing part comprises one side with a surface to which said circuit board is fixed and an opposite side with an outer surface facing away from the housing member; a secondary passage constituting part comprising a secondary passage into which part of air passing through the intake passage flows; and a flow rate detecting element placed in the secondary passage, wherein said circuit board is electrically connected to the flow rate detecting element for receiving an input of an amount of heat radiation from the flow rate detecting element, and for outputting a signal according to an air flow rate, characterized in that the base member is a resin component integrally including the board fixing part and the secondary passage constituting part providing a connection portion between the board fixing part and the secondary passage constituting part; the secondary passage constituting part constitutes the secondary passage in cooperation with the housing member; a rib (231-233, 235) is provided for improving the strength of the base member; the rib (231-233, 235) is formed integrally and protrudes from the outer surface of the board fixing part facing away from the housing member; and the rib (231-233, 235) extends along at least a part of the board fixing part to at least the connection portion.