Abstract: A modular circuit device is provided with a first circuit module including a circuit board and first and first bridge elements. The circuit board includes a substrate, a female header, and a pin header. The substrate includes a first projection at one end with the female header disposed thereon, and a second projection at the other end with the pin header disposed thereon. The first bridge member includes a bottom recess, two cavities on two sides of the bottom recess respectively, and a socket on one end of the first bridge member. The first bridge element includes a bottom recess, two cavities on two sides of the bottom recess respectively, and a projecting element at the other end of the first bridge element. The first projection is disposed in the cavities of the first bridge member. The second projection is in the cavities of the first bridge element.