Abstract: There is provided an N×N optical switch configured by connection between output ports of input side optical switches and input ports of output side optical switches by using optical waveguides on the same substrate and capable of reducing the crossing loss in a port connected to an optical waveguide having a maximum number of crossings and a higher crossing loss. In a 4×4 optical switch (10) having four input side 1×4 optical switches (SW11-SW14) each having four output ports (P1-P4), four output side 4×1 optical switches (SW21-SW24) each having four input ports (Q1-Q4), and connection optical waveguides (OW) connecting the output ports and the input ports, part of the connection optical waveguides OW are allowed to cross two or more of the other connection optical waveguides OW in one point.