To improve rigidity of a crank shaft receiving part, and prevent deformation by arranging a block side sleeve groove having a diameter larger than that of a crank shaft receiving surface and a cap side sleeve groove on a cylinder block and a bearing cap, and arranging iron made sleeves respectively.

A crank shaft 8 is supported by bearing surfaces 10, 12 of a block side and a cap side formed in a semicircular shape on a cylinder block 4 and a bearing cap 6. In this case, sleeve grooves 14, 16 having a diameter larger than that of each crank shaft receiving surfaces 10, 12 are formed on the cylinder block 4 and the bearing cap 6, and sleeves 18 are fit to the sleeve grooves 14, 16 by means of press-in. The sleeve 18 is formed of iron of cast iron and the like, it is formed of first and second sleeves 20, 22 which are divided into two parts in a semicircular shape, fastening force of a fastening bolt 28 is shared by respective sleeves 20, 22, and thereby, it is possible to improve rigidity of laminating surface 26, and also it is possible to suppress deformation of the laminating surface 26 part.