A method of manufacturing an optical connector comprising: at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) fixing and holding a plurality of multi-core optical fibers (21-2k) in a state where a position in a direction orthogonal to an optical axis of each multi-core optical fiber (21-2k) and a rotation angle around the optical axis are in a predetermined state; and a ferrule comprising an accommodating portion accommodating the at least one multi-core block (41-44 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) arranged in an mxn matrix, wherein: the cross-sectional shape of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) is an axb rectangle having a clearance of Δa and Δb with respect to a design value, and the cross-sectional shape of the accommodating portion of the ferrule is an xxy rectangle, wherein Δa and Δb are defined by the following equations Δa = (x - ma)/m and Δb = (y- nb)/n; characterized in that the number m×n of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) to be accommodated in the accommodating portion of the ferrule is determined so that the allowable rotation angle of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) in the accommodating portion of the ferrule satisfies both the following formulas and . sin − 1 a + m Δ a a 2 + b 2 − sin − 1 a a 2 + b 2 ≤ Allowable rotation angle sin − 1 a a 2 + b 2 − cos − 1 b + n Δ b a 2 + b 2 ≤ Allowable rotation angle at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) fixing and holding a plurality of multi-core optical fibers (21-2k) in a state where a position in a direction orthogonal to an optical axis of each multi-core optical fiber (21-2k) and a rotation angle around the optical axis are in a predetermined state; and a ferrule comprising an accommodating portion accommodating the at least one multi-core block (41-44 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) arranged in an mxn matrix, wherein: the cross-sectional shape of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) is an axb rectangle having a clearance of Δa and Δb with respect to a design value, and the cross-sectional shape of the accommodating portion of the ferrule is an xxy rectangle, wherein Δa and Δb are defined by the following equations Δa = (x - ma)/m and Δb = (y- nb)/n; characterized in that the number m×n of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) to be accommodated in the accommodating portion of the ferrule is determined so that the allowable rotation angle of the at least one multi-core block (41-44; 30; 51-5 mxn ; 61-6 mxn ; 71-7 mxn ; 81-8 mxn ; 91-9 mxn ; 90) in the accommodating portion of the ferrule satisfies both the following formulas and . sin − 1 a + m Δ a a 2 + b 2 − sin − 1 a a 2 + b 2 ≤ Allowable rotation angle sin − 1 a a 2 + b 2 − cos − 1 b + n Δ b a 2 + b 2 ≤ Allowable rotation angle <EOS>