A thermal flowmeter of a fluid, comprising: a flow rate measuring element disposed in a fluid passage and including a heating resistor generating heat with supply of a current, a temperature compensation resistor for detecting a fluid temperature, a first temperature measuring resistor for measuring a temperature upstream of said heating resistor, and a second temperature measuring resistor for measuring a temperature downstream of said heating resistor, all of said resistors being formed on the same substrate; a temperature control circuit (12, 13) for controlling a temperature of said heating resistor; a casing supported to a wall surface of an intake pipe forming said fluid passage and supporting said flow rate measuring element; a temperature sensor for measuring a temperature in said casing; a computing unit (17, 18) for receiving signals corresponding to a fluid flow rate from said first and second temperature detecting resistors (9, 10), performing correction depending on temperature by using said temperature sensor, and outputting the corrected result; and characterised in further comprising heating temperature control means (7, 8, 6a, 6b, 29) adapted to controlling a difference between the fluid temperature and the temperature of said heating resistor to be lowered as the fluid temperature rises; a circuit board, said temperature control circuit (12, 13), said temperature sensor, said computing unit (17, 18), and said heating temperature control means (6b, 29) being formed on said circuit board; a mount support portion for mounting said casing on an intake passage; and an electric, connecting portion for connecting said flow rate measuring element and said circuit board, wherein said temperature sensor is arranged between said mount support portion and said flow rate measuring element. a flow rate measuring element disposed in a fluid passage and including a heating resistor generating heat with supply of a current, a temperature compensation resistor for detecting a fluid temperature, a first temperature measuring resistor for measuring a temperature upstream of said heating resistor, and a second temperature measuring resistor for measuring a temperature downstream of said heating resistor, all of said resistors being formed on the same substrate; a temperature control circuit (12, 13) for controlling a temperature of said heating resistor; a casing supported to a wall surface of an intake pipe forming said fluid passage and supporting said flow rate measuring element; a temperature sensor for measuring a temperature in said casing; a computing unit (17, 18) for receiving signals corresponding to a fluid flow rate from said first and second temperature detecting resistors (9, 10), performing correction depending on temperature by using said temperature sensor, and outputting the corrected result; and characterised in further comprising heating temperature control means (7, 8, 6a, 6b, 29) adapted to controlling a difference between the fluid temperature and the temperature of said heating resistor to be lowered as the fluid temperature rises; a circuit board, said temperature control circuit (12, 13), said temperature sensor, said computing unit (17, 18), and said heating temperature control means (6b, 29) being formed on said circuit board; a mount support portion for mounting said casing on an intake passage; and an electric, connecting portion for connecting said flow rate measuring element and said circuit board, wherein said temperature sensor is arranged between said mount support portion and said flow rate measuring element.