PURPOSE: To improve the assembling operability by providing a stage caulking and fixing an input terminal to a base of an input stage section chamber and a stage assembling a sub-assembly for input stage where a circuit component is assembled and wired in advance into the input section chamber.

CONSTITUTION: A shield section plate 2 to section chambers A'... is soldered in the base 1. Then the input terminal 7 is caulked and fixed to the base 1. It is not required for the necessity of soldering by means of the fixing through the caulking, the terminal 7 is fixed stably and the reliability is improved. Then the input circuit sub-assembly 11 where the circuit component 10 and a minute sectioning shield section plate 2' are fitted onto a board 5 is prepared, the sub- assembly 11 is assembled into the input stage section chamber A' being a space in the base 1 and soldered so as to complete the input stage sectioning chamber A'. The input terminal of caulking type is cheaper than the terminal of screw tightening type, the terminal is fixed to the base with one-touch and the assembling operability is improved.