A laser processing apparatus for forming a modified region which functions as a starting point for cutting within an object to be cut along a line along which the object is intended to be cut, comprising: a stage (109, 111, 113) adapted for mounting the object; a laser source for emitting the laser light at a wavelength, which can be choosen according to a light absorption characteristic of the object, to which the object is transparent or exhibits a low absorption; a converging lens for converging the laser light emitted from the laser source within the object which is mounted on the stage (109, 111, 113) to form the modified region at a converging point of the laser light; and characterized by: a controller having a function of moving at least one of the stage (109, 111, 113)and the converging lens by a first amount in a thickness direction of the object with reference to a laser light entrance surface of the object so that the converging point of the laser light is positioned within the object, moving the stage (109, 111 113) in a direction perpendicular to the thickness direction of the object to be processed so that the converging point of the laser light moves along the line along which the object is intended to be cut, thereafter moving at least one of the stage (109, 111, 113) and the converging lens by a second amount in the thickness direction of the object with reference to the laser light incident surface, and moving the stage in a direction perpendicular to the thickness direction of the object so that the converging point of the laser light moves along the line along which the object is intended to be cut; a determining means for determining the light absorption characteristic of the object to be cut by measuring the light absorption characteristic of the object; and a measuring means for measuring the thickness of the object to be cut. a stage (109, 111, 113) adapted for mounting the object; a laser source for emitting the laser light at a wavelength, which can be choosen according to a light absorption characteristic of the object, to which the object is transparent or exhibits a low absorption; a converging lens for converging the laser light emitted from the laser source within the object which is mounted on the stage (109, 111, 113) to form the modified region at a converging point of the laser light; and characterized by: a controller having a function of moving at least one of the stage (109, 111, 113)and the converging lens by a first amount in a thickness direction of the object with reference to a laser light entrance surface of the object so that the converging point of the laser light is positioned within the object, moving the stage (109, 111 113) in a direction perpendicular to the thickness direction of the object to be processed so that the converging point of the laser light moves along the line along which the object is intended to be cut, thereafter moving at least one of the stage (109, 111, 113) and the converging lens by a second amount in the thickness direction of the object with reference to the laser light incident surface, and moving the stage in a direction perpendicular to the thickness direction of the object so that the converging point of the laser light moves along the line along which the object is intended to be cut; a determining means for determining the light absorption characteristic of the object to be cut by measuring the light absorption characteristic of the object; and a measuring means for measuring the thickness of the object to be cut. a controller having a function of moving at least one of the stage (109, 111, 113)and the converging lens by a first amount in a thickness direction of the object with reference to a laser light entrance surface of the object so that the converging point of the laser light is positioned within the object, moving the stage (109, 111 113) in a direction perpendicular to the thickness direction of the object to be processed so that the converging point of the laser light moves along the line along which the object is intended to be cut, thereafter moving at least one of the stage (109, 111, 113) and the converging lens by a second amount in the thickness direction of the object with reference to the laser light incident surface, and moving the stage in a direction perpendicular to the thickness direction of the object so that the converging point of the laser light moves along the line along which the object is intended to be cut; a determining means for determining the light absorption characteristic of the object to be cut by measuring the light absorption characteristic of the object; and a measuring means for measuring the thickness of the object to be cut.