A semiconductor laser device of the present disclosure includes a cooling plate, an insulating sheet, a first cooling block, and a first semiconductor laser element. The conductive cooling plate includes a water supply passage and a drain passage. The insulating sheet is provided to the cooling plate, and includes a first through hole connected to the water supply passage and a second through hole connected to the drain passage. A first cooling block is provided to the insulating sheet, includes therein a first tube connected to the first through hole and the second through hole, and is electrically conductive. The first semiconductor laser element is provided to the first cooling block. The first semiconductor laser element includes a first electrode, and a second electrode opposite to the first electrode. The first electrode is electrically connected to the first cooling block, and the cooling plate is at a floating potential.