A laser machining device which condenses a laser light inside a wafer and forms modified regions in a plurality of layers in the wafer, includes an infrared imaging optical system configured to face one surface of the wafer. In a case where a modified region positioned on a side of another surface opposite to the one surface of the wafer is defined as a first modified region and another modified region is defined as a second modified region, among the modified regions in the plurality of layers, the infrared imaging optical system has a focusing range that includes the first modified region and the another surface, and simultaneously images the first modified region and the another surface, and the second modified region is positioned outside the focusing range.