A method of producing a multi-piece wiring substrate array (10a, 10b), the multi-piece wiring substrate array (10a, 10b) comprising: a product region which is formed of a ceramic material, which has a front surface and a back surface and has a rectangular shape in plan view, and which has a plurality of wiring substrate units that are adjacently arranged in a matrix form; an edge portion which is formed of the ceramic material, which is located around the product region, and which has a front surface and a back surface and has a rectangular frame shape in plan view; and dividing grooves (16, 18) which are formed on at least one of the front surface and the back surface of the wiring substrate array and are arranged in a lattice shape in plan view, and which are provided between adjacent wiring substrate units and between the product region and the edge portion, the method comprising: a step of forming a plurality of dividing grooves (16, 18) in at least one of a front surface and a back surface of a green sheet (gs) which has a rectangular shape in plan view and which is to become the multi-piece wiring substrate array having the product region and the edge portion, by irradiating with a laser beam a plurality of times (1st to 4th) so that the dividing grooves (16, 18) are provided around a portion of the green sheet corresponding to the wiring substrate units and between portions of the green sheet corresponding to the product region and the edge portion, and so that the dividing grooves (16, 18) are arranged in a lattice shape in plan view; characterised in that: a plurality of laser beam irradiation processes (1st to 4th) are carried out while scanning the laser beam thereon, and by gradually shifting the focal point of the laser beam so that the depth of the focal point, as measured from the front surface or back surface of the green sheet (gs), in a laser irradiation process is greater than that in the preceding laser irradiation process. a product region which is formed of a ceramic material, which has a front surface and a back surface and has a rectangular shape in plan view, and which has a plurality of wiring substrate units that are adjacently arranged in a matrix form; an edge portion which is formed of the ceramic material, which is located around the product region, and which has a front surface and a back surface and has a rectangular frame shape in plan view; and dividing grooves (16, 18) which are formed on at least one of the front surface and the back surface of the wiring substrate array and are arranged in a lattice shape in plan view, and which are provided between adjacent wiring substrate units and between the product region and the edge portion, the method comprising: a step of forming a plurality of dividing grooves (16, 18) in at least one of a front surface and a back surface of a green sheet (gs) which has a rectangular shape in plan view and which is to become the multi-piece wiring substrate array having the product region and the edge portion, by irradiating with a laser beam a plurality of times (1st to 4th) so that the dividing grooves (16, 18) are provided around a portion of the green sheet corresponding to the wiring substrate units and between portions of the green sheet corresponding to the product region and the edge portion, and so that the dividing grooves (16, 18) are arranged in a lattice shape in plan view; characterised in that: a plurality of laser beam irradiation processes (1st to 4th) are carried out while scanning the laser beam thereon, and by gradually shifting the focal point of the laser beam so that the depth of the focal point, as measured from the front surface or back surface of the green sheet (gs), in a laser irradiation process is greater than that in the preceding laser irradiation process. a step of forming a plurality of dividing grooves (16, 18) in at least one of a front surface and a back surface of a green sheet (gs) which has a rectangular shape in plan view and which is to become the multi-piece wiring substrate array having the product region and the edge portion, by irradiating with a laser beam a plurality of times (1st to 4th) so that the dividing grooves (16, 18) are provided around a portion of the green sheet corresponding to the wiring substrate units and between portions of the green sheet corresponding to the product region and the edge portion, and so that the dividing grooves (16, 18) are arranged in a lattice shape in plan view; characterised in that: a plurality of laser beam irradiation processes (1st to 4th) are carried out while scanning the laser beam thereon, and by gradually shifting the focal point of the laser beam so that the depth of the focal point, as measured from the front surface or back surface of the green sheet (gs), in a laser irradiation process is greater than that in the preceding laser irradiation process.