A laser cutting apparatus used for cutting a work with a laser beam (LB) that tends to become a ring beam (RB) whose inner and outer diameters gradually expand after passing a focus position (F) of a condenser lens arranged in a laser processing head (HA), wherein the apparatus comprises: a laser oscillator ; a process fiber having a first end connected to the laser oscillator ; the laser processing head (HA) provided with a collimation lens (CL) for forming a parallel beam from a laser beam (LB) emitted from a second end of the process fiber ; and the ring beam forming unit for forming the parallel beam into a ring beam (RB), and that includes the condenser lens , characterized in that said collimate lens CL is positionally adjustable along an optical axis of a laser beam (LB) so that the beam diameter of the laser beam (LB) made incident to said ring beam forming unit is freely adjustable, and in that the apparatus is configured to: apply a non-ring part of the laser beam (LB) to a surface of the work to carry out a piercing process; and thereafter, change the laser beam (LB) applying to the surface of the work to the ring beam (RB) for carrying out the laser cutting of the work by adjusting the position of the collimation lens (CL) in the direction of an optical axis of the laser beam (LB) such that the focus position (F) is brought closer to the ring beam forming unit , the condenser lens providing the ring beam (RB) with an outer diameter being in a range of 300 μm to 600 μm and an inner diameter ratio being in a range of 30% to 70%. a laser oscillator ; a process fiber having a first end connected to the laser oscillator ; the laser processing head (HA) provided with a collimation lens (CL) for forming a parallel beam from a laser beam (LB) emitted from a second end of the process fiber ; and the ring beam forming unit for forming the parallel beam into a ring beam (RB), and that includes the condenser lens , characterized in that said collimate lens CL is positionally adjustable along an optical axis of a laser beam (LB) so that the beam diameter of the laser beam (LB) made incident to said ring beam forming unit is freely adjustable, and in that the apparatus is configured to: apply a non-ring part of the laser beam (LB) to a surface of the work to carry out a piercing process; and thereafter, change the laser beam (LB) applying to the surface of the work to the ring beam (RB) for carrying out the laser cutting of the work by adjusting the position of the collimation lens (CL) in the direction of an optical axis of the laser beam (LB) such that the focus position (F) is brought closer to the ring beam forming unit , the condenser lens providing the ring beam (RB) with an outer diameter being in a range of 300 μm to 600 μm and an inner diameter ratio being in a range of 30% to 70%. apply a non-ring part of the laser beam (LB) to a surface of the work to carry out a piercing process; and thereafter, change the laser beam (LB) applying to the surface of the work to the ring beam (RB) for carrying out the laser cutting of the work by adjusting the position of the collimation lens (CL) in the direction of an optical axis of the laser beam (LB) such that the focus position (F) is brought closer to the ring beam forming unit , the condenser lens providing the ring beam (RB) with an outer diameter being in a range of 300 μm to 600 μm and an inner diameter ratio being in a range of 30% to 70%. <EOS>