PURPOSE: To provide perfect protection for strain gage resistors and the like and to also provide perfect protection of a beam body, by forming a protecting layer around a thin film resistor circuit pattern by a dipping method.

CONSTITUTION: A beam body 1 comprises holes 5 and 6 and thin deformed parts 3 and 4. A corrosion preventing layer 9 comprising a polyimide resin film, a pattern forming surface 10, an insulating film 11, a resistor layer, and a conductor layer are sequentially laminated around the entire surrounding part of the beam body 1. The layers are selectively etched. Then, strain gage resistors R1WR4 are positioned on the deformed parts 3 and 4. A thin resistor circuit pattern 14 comprising the resistors R1WR4, a lead pattern L, and the like is formed. After the formation of the pattern 14, a protecting layer 15 is formed on the approximately entire surrounding part of the beam body 1 by a dipping method. Lead wires 17 are soldered to a terminal part, which is not coated by the layer 15.