A preform manufacturing method for manufacturing a multicore optical fiber preform (3, 6) comprising a plurality of core portions each extending in a predetermined axial direction, and a common cladding portion (32, 62) covering each of the plurality of core portions, the preform manufacturing method comprising: a hole forming step of preparing a glass body to constitute a part of the common cladding portion, and perforating the glass body to form a plurality of holes each extending in the axial direction of the glass body, thereby producing a glass pipe (22, 52); and a heating integration step of preparing a plurality of core rods (21 0 -21 6, 51 1 -51 8) each including a respective core portion (31 0 -31 6, 61 1 -61 8) of the plurality of core portions, inserting each of the plurality of core rods into a respective core portion of the plurality of holes of the glass pipe, and heating the glass pipe with the plurality of core rods being inserted in the respective holes, thereby to implement integration of the plurality of core rods and the glass pipe, wherein, when as a structure parameter after the integration, d is defined as a distance between a center position of a peripheral core portion located off a central axis of the multicore optical fiber preform and the central axis of the multicore optical fiber preform, and as structure parameters before the integration, r is defined as a radius of a peripheral core rod corresponding to the peripheral core portion, R as a radius of a peripheral hole into which the peripheral core rod is to be inserted, out of the plurality of holes to be formed in the glass body, and D as a distance between a center position of the peripheral hole and the central axis of the glass body, characterized in that the hole forming step is configured to perforate the glass body to form a peripheral hole at a position satisfying the following relation on a straight line connecting the center position of the peripheral core portion and the central axis of the glass body: d < D ≦ d + R − r a hole forming step of preparing a glass body to constitute a part of the common cladding portion, and perforating the glass body to form a plurality of holes each extending in the axial direction of the glass body, thereby producing a glass pipe (22, 52); and a heating integration step of preparing a plurality of core rods (21 0 -21 6, 51 1 -51 8) each including a respective core portion (31 0 -31 6, 61 1 -61 8) of the plurality of core portions, inserting each of the plurality of core rods into a respective core portion of the plurality of holes of the glass pipe, and heating the glass pipe with the plurality of core rods being inserted in the respective holes, thereby to implement integration of the plurality of core rods and the glass pipe, wherein, when as a structure parameter after the integration, d is defined as a distance between a center position of a peripheral core portion located off a central axis of the multicore optical fiber preform and the central axis of the multicore optical fiber preform, and as structure parameters before the integration, r is defined as a radius of a peripheral core rod corresponding to the peripheral core portion, R as a radius of a peripheral hole into which the peripheral core rod is to be inserted, out of the plurality of holes to be formed in the glass body, and D as a distance between a center position of the peripheral hole and the central axis of the glass body, characterized in that the hole forming step is configured to perforate the glass body to form a peripheral hole at a position satisfying the following relation on a straight line connecting the center position of the peripheral core portion and the central axis of the glass body: d < D ≦ d + R − r