A light-guiding device, comprising: a group of mirrors (M1-M10) that converts a first beam bundle consisting of a plurality of laser beams, each of which has an optical axis aligned in a first plane and an F axis that intersects with the first plane, into a second beam bundle consisting of a plurality of laser beams, each of which has an optical axis aligned in a second plane and an F axis that extends along the second plane; a group of collimating lenses (C1-C10) provided at a stage previous to the group of mirrors (M1-M10) and consisting of collimating lenses (Ci) each of which collimates a divergence, in an F-axis direction, of a corresponding one of the plurality of laser beams constituting the first beam bundle; a converging lens provided at a stage subsequent to the group of mirrors (M1-M10), the converging lens converging the second beam bundle by refracting each of the plurality of laser beams constituting the second beam bundle, a substrate having an upper surface parallel to the first plane; and a group of supporting columns (P1-P10) consisting of supporting columns each of which (Pi) supports a corresponding one (Ci) of the collimating lenses constituting the group of collimating lenses (C1-C10) and has (i) a side surface to which a side surface of the corresponding one (Ci) of the collimating lenses (C1-C10) is bonded and fixed by a first resin and (ii) a bottom surface which is bonded and fixed to an upper surface of the substrate by a second resin, the group of mirrors (M1-M10) consisting of double mirrors (Mi) each of which includes (i) a first mirror that reflects a corresponding one of the plurality of laser beams constituting the first beam bundle and (ii) a second mirror that reflects a laser beam reflected by the first mirror, a traveling direction of each of the laser beams constituting the second beam bundle at a portion where the second beam bundle has not been converged by the converging lens being given an offset, by setting an orientation of the second mirror, so as to be offset from a reference direction, so as to counter a change in the traveling direction away from the reference direction caused by an expansion of the first and the second resins (R2, R1), the reference direction being a traveling direction of each of the laser beams constituting the second beam bundle at the portion where the second beam bundle has not been converged by the converging lens when the plurality of laser beams constituting the second beam bundle at a portion where the second beam bundle has been converged by the converging lens forms a single intersection on an optical axis of the converging lens. a group of mirrors (M1-M10) that converts a first beam bundle consisting of a plurality of laser beams, each of which has an optical axis aligned in a first plane and an F axis that intersects with the first plane, into a second beam bundle consisting of a plurality of laser beams, each of which has an optical axis aligned in a second plane and an F axis that extends along the second plane; a group of collimating lenses (C1-C10) provided at a stage previous to the group of mirrors (M1-M10) and consisting of collimating lenses (Ci) each of which collimates a divergence, in an F-axis direction, of a corresponding one of the plurality of laser beams constituting the first beam bundle; a converging lens provided at a stage subsequent to the group of mirrors (M1-M10), the converging lens converging the second beam bundle by refracting each of the plurality of laser beams constituting the second beam bundle, a substrate having an upper surface parallel to the first plane; and a group of supporting columns (P1-P10) consisting of supporting columns each of which (Pi) supports a corresponding one (Ci) of the collimating lenses constituting the group of collimating lenses (C1-C10) and has (i) a side surface to which a side surface of the corresponding one (Ci) of the collimating lenses (C1-C10) is bonded and fixed by a first resin and (ii) a bottom surface which is bonded and fixed to an upper surface of the substrate by a second resin, the group of mirrors (M1-M10) consisting of double mirrors (Mi) each of which includes (i) a first mirror that reflects a corresponding one of the plurality of laser beams constituting the first beam bundle and (ii) a second mirror that reflects a laser beam reflected by the first mirror, a traveling direction of each of the laser beams constituting the second beam bundle at a portion where the second beam bundle has not been converged by the converging lens being given an offset, by setting an orientation of the second mirror, so as to be offset from a reference direction, so as to counter a change in the traveling direction away from the reference direction caused by an expansion of the first and the second resins (R2, R1), the reference direction being a traveling direction of each of the laser beams constituting the second beam bundle at the portion where the second beam bundle has not been converged by the converging lens when the plurality of laser beams constituting the second beam bundle at a portion where the second beam bundle has been converged by the converging lens forms a single intersection on an optical axis of the converging lens.