PURPOSE: To reduce the cost and weight of a circuit unit by forming board holding pieces for holding a circuit board therebetween and sheet inside bent pieces on the bottom of an upper case or top of a lower case and sheet outside bent pieces on the top of the lower case or bottom of the upper case.

CONSTITUTION: An electromagnetic wave shielded circuit unit 1 is composed of a circuit board 2 and flattened rectangular shield case 3. A synthetic resin upper and lower cases 4 and 5 are formed as an upper and lower halves of a shield case 3. On a central part of the top of the case 5, two sets of board holding pieces 5a are formed and two vertically up directed sheet inside bent pieces 5b are formed near each piece 5a. On a central part of the bottom of the case 4, board hold pieces 4a are formed at positions corresponding to the pieces 5a and two vertically down directed sheet outside bent pieces 4b are formed near each piece 4a.