A midsole which reduces a load applied to a knee, the midsole comprising: a) a first soft portion which is formed at a front side based on an arch portion of a foot; b) a second soft portion which is formed at a rear side based on the arch portion of the foot; and c) a hard portion which is formed in a region of the arch portion of the foot, and has greater hardness than the first and second soft portions, d1) the first soft portion and the second soft portion are spaced apart from each other in a forward and rearward direction based on a foot arch region, wherein d2) the first soft portion and the second soft portion are formed in an inner region of the foot, e) the hard portion is formed at the arch portion of the foot and at a front outer side and a rear outer side of the arch portion and in the remaining region except for the first and second soft portions (11, 13), f) the first soft portion is formed at the front inner side and in the front inner side region including a big toe portion, g) the second soft portion is formed at the rear inner side and in the rear inner side region including an inner side of a heel, h) the soft portion (11, 13) and the hard portion have inclined cross sections (11a, 13a, 15a, 15b) that are vertically joined together, respectively, and i) a value of hardness in a region where the soft portion (11, 13) and the hard portion are joined together is between a value of hardness of the soft portions and a value of hardness of the hard portion, and j) an arch shank, which has greater hardness than the hard portion, is installed in a region of the hard portion which corresponds to the arch portion of the foot. a) a first soft portion which is formed at a front side based on an arch portion of a foot; b) a second soft portion which is formed at a rear side based on the arch portion of the foot; and c) a hard portion which is formed in a region of the arch portion of the foot, and has greater hardness than the first and second soft portions, d1) the first soft portion and the second soft portion are spaced apart from each other in a forward and rearward direction based on a foot arch region, wherein d2) the first soft portion and the second soft portion are formed in an inner region of the foot, e) the hard portion is formed at the arch portion of the foot and at a front outer side and a rear outer side of the arch portion and in the remaining region except for the first and second soft portions (11, 13), f) the first soft portion is formed at the front inner side and in the front inner side region including a big toe portion, g) the second soft portion is formed at the rear inner side and in the rear inner side region including an inner side of a heel, h) the soft portion (11, 13) and the hard portion have inclined cross sections (11a, 13a, 15a, 15b) that are vertically joined together, respectively, and i) a value of hardness in a region where the soft portion (11, 13) and the hard portion are joined together is between a value of hardness of the soft portions and a value of hardness of the hard portion, and j) an arch shank, which has greater hardness than the hard portion, is installed in a region of the hard portion which corresponds to the arch portion of the foot.