PURPOSE: To obtain a multi-input OR circuit which has equal input sensitivity among input terminals and outputs a large current, by forming Josephson junctions at more than one point and by performing OR operation at each junction.

CONSTITUTION: Josephson junctions J1 and J2 are connected in series to resistances r1 and r2, and the series circuits are connected mutually in parallel and supplied with a bias current IB. If r1=r2, the bias currents IB1 and IB2 of the junctions are equal to each other and when input signal currents IH1 and IH2 are zero, those bias currents are set a little bit less than the critical current values of the Josephson joints, so that when the currents IH1 and IH2 are both zero, almost all of the current IB flows through the junctions J1 and J2. Then, flowing the current IH1 develops a voltage at the junction J1. Consequently, almost all of the bias current flowing through the junction J1 flows through the junction J2. As a result, a voltage is developed at the junction J2 as well. Therefore, almost all of the current IB flows out from an output terminal Out. When the current IH2 flows, and when IH1 and IH2 flow, the operation is the same, and thus this circuit performs OR operation.