A thermal flow sensor can adjust the temperature of a heating element in a highly precise and reliable manner with the use of simple circuits, devices and process steps. The sensor includes an amplifier section (7) that amplifies a voltage across opposite ends of at least one of resistors (3, 4, 5) that constitute a bridge circuit, a current control section (9) that is controlled based on an output voltage of the amplifier section (7), and an output terminal (14) that is connected to one end of a heating element (1) that is controlled to be energized by the current control section (9). The amplifier section (7) includes an amplification factor control section for controlling an amplification factor by an electric signal from a computer, and uses an output voltage which has been amplified and impressed to an input voltage to an operational amplifier (8).