A thermal flowmeter (1, 1A) having a sensor channel over which resistors for measuring a flow rate are mounted bridgewise and a bypass channel relative to the sensor channel, comprising: a body with first and second channels (43, 45) at opposing end faces thereof and a channel space formed therein, the body having the shape of a rectangular parallelepiped and being symmetric right and left of a central axis; whereby the first and second channels (43, 45) communicate with the channel space, and the channel space forms the bypass channel and the sensor channel; a laminate (50, 50A) fitted in the channel space, the laminate (50, 50A) being formed by a plurality of thin sheets (51, 52) each having an opening; a substrate having first electrodes on a surface thereof; wherein the laminate (50, 50A) is adapted to divide a fluid into a fluid portion flowing into the sensor channel and a fluid portion flowing into the bypass channel; wherein a measurement chip is mounted on the substrate and comprises a first temperature sensing resistor and a second temperature sensing resistor disposed in the sensor channel, wherein the first and second temperature sensing resistors (R1, R2) are arranged along a flow direction in the sensor channel; a heating resistor (Rh) disposed between the first and second sensing resistors (R1, R2) to heat the first and second temperature sensing resistors (R1, R2), and a fluid temperature sensing resistor (Rt) for sensing the temperature of a fluid under measurement; wherein the measurement chip comprises second electrodes for the resistors, wherein the second electrodes are bonded to respective ones of first electrodes; and an electric circuit configured for control so that the heating resistor (Rh) and the fluid temperature sensing resistor (Rt) show a constant difference in temperature; means for measuring the flow rate of the fluid under measurement based on a temperature difference between the first and second temperature sensing resistors (R1, R2); wherein the laminate includes mesh sheets each of which is formed by a thin sheet and has a mesh portion at both ends of the sheet, the mesh portions communicating with the first and second channels (43, 45), respectively, and the mesh sheets are laminated one on another through a spacer; and wherein the bypass channel is formed by the substrate being in close contact with the body so as to close the channel space through the laminate (50, 50A), wherein the sensor channel is defined by a groove (13, 23) formed in at least one of a measurement chip and the substrate; and wherein the flowmeter is adapted to measure flow of a fluid in a forward direction or a reverse direction. a body with first and second channels (43, 45) at opposing end faces thereof and a channel space formed therein, the body having the shape of a rectangular parallelepiped and being symmetric right and left of a central axis; whereby the first and second channels (43, 45) communicate with the channel space, and the channel space forms the bypass channel and the sensor channel; a laminate (50, 50A) fitted in the channel space, the laminate (50, 50A) being formed by a plurality of thin sheets (51, 52) each having an opening; a substrate having first electrodes on a surface thereof; wherein the laminate (50, 50A) is adapted to divide a fluid into a fluid portion flowing into the sensor channel and a fluid portion flowing into the bypass channel; wherein a measurement chip is mounted on the substrate and comprises a first temperature sensing resistor and a second temperature sensing resistor disposed in the sensor channel, wherein the first and second temperature sensing resistors (R1, R2) are arranged along a flow direction in the sensor channel; a heating resistor (Rh) disposed between the first and second sensing resistors (R1, R2) to heat the first and second temperature sensing resistors (R1, R2), and a fluid temperature sensing resistor (Rt) for sensing the temperature of a fluid under measurement; wherein the measurement chip comprises second electrodes for the resistors, wherein the second electrodes are bonded to respective ones of first electrodes; and an electric circuit configured for control so that the heating resistor (Rh) and the fluid temperature sensing resistor (Rt) show a constant difference in temperature; means for measuring the flow rate of the fluid under measurement based on a temperature difference between the first and second temperature sensing resistors (R1, R2); wherein the laminate includes mesh sheets each of which is formed by a thin sheet and has a mesh portion at both ends of the sheet, the mesh portions communicating with the first and second channels (43, 45), respectively, and the mesh sheets are laminated one on another through a spacer; and wherein the bypass channel is formed by the substrate being in close contact with the body so as to close the channel space through the laminate (50, 50A), wherein the sensor channel is defined by a groove (13, 23) formed in at least one of a measurement chip and the substrate; and wherein the flowmeter is adapted to measure flow of a fluid in a forward direction or a reverse direction.