A circuit includes a first input and output terminals to which a current, a voltage, or an electromagnetic wave (referred to as “current or the like” below) is applied, a second input and output terminals to which the current or the like is applied, a first board including a matrix circuit which is formed by a first line and includes a 90-degree hybrid circuit and a delay line, the first line in which one end is connected to the first input and output terminals and a tip of the other end is opened, a second board including a second line in which one end is connected to the second input and output terminals, and a tip of the other end is opened, and a shielding plate including an opening portion.