CONTINUOUS CASTING MACHINE BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a continuous casting machine having support rollers arranged to face each other so that a slab passage is interposed between the support rollers. Priority is claimed on Japanese Patent Application No. 2009-097681, filed April 14,2009, the content of which is incorporated herein by reference. Description of Related Art [0002] A continuous casting machine for manufacturing a slab from a molten metal includes a slab passage through which a slab formed in a mold passes from a tundish, and a pair of roller groups arranged to face each other so that the slab passage is interposed between the roller groups. The roller group has a plurality of support rollers which guide the slab, and the support rollers are arranged in a casting direction of the slab. Each support roller is installed to be rotatable based on a central shaft extending in a width direction of the slab so that the slab is taken out and carried in a predetermined casting direction while being supported between the support rollers. Each support roller rotates along with the movement of the slab so as to guide the slab smoothly. [0003] In the continuous casting machine, below the mold, bulging may occur at the slab due to a positive pressure of non-solidified molten steel. In particular, since both ends of the aforementioned support roller are supported by bearings, an amount of bulging is increased near a center portion of the slab in a width direction when the support roller is bent near the center portion in the width direction of the slab. For this reason, in order to decrease the amount of bulging, the support roller is conventionally divided into a plurality of divided rollers in a width direction of the slab so that the divided rollers are supported by intermediate bearings (Patent Document 1). [0004] In addition, in order to suppress the bulging, since the slab has a solid fraction corresponding to 0.3-0.9 during the continuous casting process, it has also been proposed to make a distance between the support rollers downstream smaller than a distance between support rollers upstream (Patent Document 2). Patent Document [0005] [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2007-30012 [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2005-193265 SUMMARY OF THE INVENTION Technical Problem [0006] However, the inventors found by investigation that bulging may be suppressed insufficiently in some cases only when the support roller is just divided into a plurality of divided rollers. For example, between divided rollers of a single support roller, which are adjacent to each other in a width direction of the slab, there is a non-supporting region where the roller does not contact the slab. Even though the divided rollers are disposed at regular intervals, it was found that the amount of bulging may not be suppressed at the non-supporting region in some cases, and thus the bulging is not always suppressed sufficiently. In addition, center segregation, which is an internal defect of the slab, is generated due to the bulging, which deteriorates the quality of the slab. [0007] The present invention is made in consideration of the above, and an object of the present invention is to suppress center segregation of a slab by decreasing an amount of bulging of the slab. Solution to Problem [0008] In order to accomplish the above object, in one aspect of the present invention, there is provided a continuous casting machine, which includes a plurality of support rollers arranged to face each other so that a passage of a slab is interposed between the support rollers, wherein each of the support rollers has a plurality of divided rollers arranged in a width direction of the slab, and wherein, for each of the support roller disposed at a location on the passage where the slab has a central solid fraction equal to or greater than 0.2 and smaller than 1.0 during a continuous casting process: when a distance between the divided rollers of the support roller, which are adjacent to each other in the width direction of the slab, is defined as a distance A mm, and when a distance between (i) a support roller adjacent to an upstream side in a casting direction and (ii) another support roller adjacent to a downstream side in the casting direction is defined as a distance B mm, the distance A and the distance B satisfy the following equations (1) and (2): A<0.001xB2-1.5xB+735-- (1) 400