A multiplexer comprising: an output section being constituted by: a group of laser light sources (LDi) generating an input beam bundle made of a plurality of laser beams whose optical axes are contained in a single plane; and a group of mirrors being made of double mirrors (Mi) reflecting the plurality of laser beams constituting the input beam bundle generated by the group of laser light sources, each of the double mirrors (Mi), constituting the group of mirrors, being constituted by a first mirror mounted on a specific flat surface and a second mirror mounted on the first mirror, the first mirror having a first reflective surface which reflects a corresponding one of the plurality of laser beams generated by the group of laser light sources, the second mirror having a second reflective surface which reflects the corresponding one laser beam that has been reflected by the first reflective surface, the group of laser light sources being located so that respective emission edge surfaces of the plurality of laser light sources face in a specific direction, the first mirror being oriented so that a projection, on the specific flat surface, of a normal vector of the first reflective surface faces opposite to the specific direction, the second mirror being oriented so that optical axes of the plurality of laser beams that have been reflected by the second reflective surface intersect with each other at a single point; the output section outputting an output beam bundle made of a plurality of laser beams whose optical axes are contained in a second single plane parallel to the single plane, each of the plurality of laser beams having an F-axis that is not orthogonal to the second single plane; the multiplexer further comprising: a converging lens converging the output beam bundle outputted from the output section, wherein the double mirrors (Mi) are arranged such that extensions of the optical axes of the plurality of laser beams at a portion where the output beam bundle has been outputted from the output section but has not been converged by the converging lens intersect with each other at a single point, and an intersection of the plurality of laser beams at a portion where the output beam bundle has been converged by the converging lens is formed at a position that is closer to the converging lens than a focal point of the converging lens is. a group of laser light sources (LDi) generating an input beam bundle made of a plurality of laser beams whose optical axes are contained in a single plane; and a group of mirrors being made of double mirrors (Mi) reflecting the plurality of laser beams constituting the input beam bundle generated by the group of laser light sources, each of the double mirrors (Mi), constituting the group of mirrors, being constituted by a first mirror mounted on a specific flat surface and a second mirror mounted on the first mirror, the first mirror having a first reflective surface which reflects a corresponding one of the plurality of laser beams generated by the group of laser light sources, the second mirror having a second reflective surface which reflects the corresponding one laser beam that has been reflected by the first reflective surface, the group of laser light sources being located so that respective emission edge surfaces of the plurality of laser light sources face in a specific direction, the first mirror being oriented so that a projection, on the specific flat surface, of a normal vector of the first reflective surface faces opposite to the specific direction, the second mirror being oriented so that optical axes of the plurality of laser beams that have been reflected by the second reflective surface intersect with each other at a single point; the output section outputting an output beam bundle made of a plurality of laser beams whose optical axes are contained in a second single plane parallel to the single plane, each of the plurality of laser beams having an F-axis that is not orthogonal to the second single plane; the multiplexer further comprising: a converging lens converging the output beam bundle outputted from the output section, wherein the double mirrors (Mi) are arranged such that extensions of the optical axes of the plurality of laser beams at a portion where the output beam bundle has been outputted from the output section but has not been converged by the converging lens intersect with each other at a single point, and an intersection of the plurality of laser beams at a portion where the output beam bundle has been converged by the converging lens is formed at a position that is closer to the converging lens than a focal point of the converging lens is. a converging lens converging the output beam bundle outputted from the output section, wherein the double mirrors (Mi) are arranged such that extensions of the optical axes of the plurality of laser beams at a portion where the output beam bundle has been outputted from the output section but has not been converged by the converging lens intersect with each other at a single point, and an intersection of the plurality of laser beams at a portion where the output beam bundle has been converged by the converging lens is formed at a position that is closer to the converging lens than a focal point of the converging lens is.