A laser processing apparatus comprising: a laser oscillation portion; a laser emission unit including an emission optical system (18, 22, 23) that emits a laser beam oscillated by the laser oscillation portion; and a laser radiation unit that is detachably connected to the laser emission unit and has a radiation optical system (41, 43) for radiating the laser beam emitted from the laser emission unit to an object to be processed, a first connection portion provided in a part of the laser emission unit that is connected to the laser radiation unit; a second connection portion provided in a part of the laser radiation unit that is connected to the laser emission unit; a projection provided on a lower end portion of one of the first connection portion and the second connection portion, the projection protruding along an optical axis of the laser beam; and a recess provided on a lower end portion of the other one of the first connection portion and the second connection portion, wherein the recess, when connecting the laser emission unit with the laser radiation unit, fits the projection and slidably guides the projection along the optical axis, the recess is open in a direction facing at least the projection in an optical axis direction wherein one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) includes a protrusion that protrudes from a corresponding connection portion toward the other one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) along the optical axis, the other one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) includes an accommodation portion, which is dented from a corresponding connection portion in a protruding direction of the protrusion along the optical axis, the laser processing apparatus being characterized in that the recess is open downward in a direction intersecting the optical axis and a protruding length of the projection is greater than a protruding length of the protrusion. a laser oscillation portion; a laser emission unit including an emission optical system (18, 22, 23) that emits a laser beam oscillated by the laser oscillation portion; and a laser radiation unit that is detachably connected to the laser emission unit and has a radiation optical system (41, 43) for radiating the laser beam emitted from the laser emission unit to an object to be processed, a first connection portion provided in a part of the laser emission unit that is connected to the laser radiation unit; a second connection portion provided in a part of the laser radiation unit that is connected to the laser emission unit; a projection provided on a lower end portion of one of the first connection portion and the second connection portion, the projection protruding along an optical axis of the laser beam; and a recess provided on a lower end portion of the other one of the first connection portion and the second connection portion, wherein the recess, when connecting the laser emission unit with the laser radiation unit, fits the projection and slidably guides the projection along the optical axis, the recess is open in a direction facing at least the projection in an optical axis direction wherein one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) includes a protrusion that protrudes from a corresponding connection portion toward the other one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) along the optical axis, the other one of the emission optical system (18, 22, 23) and the radiation optical system (41, 43) includes an accommodation portion, which is dented from a corresponding connection portion in a protruding direction of the protrusion along the optical axis, the laser processing apparatus being characterized in that the recess is open downward in a direction intersecting the optical axis and a protruding length of the projection is greater than a protruding length of the protrusion.