This study is devoted to clarifying change of flow characteristics as the shape of a circular cylinder is modified with dimples in the laminar flow regime. The investigation is performed numerically in a two-dimensional framework. The cylinder is represented by an immersed boundary method and marker particles on a Cartesian grid system. The number and location of dimples are the key parameters. The analysis on the flow pattern and flow-induced forces is performed at Re=40 and 50. Furthermore, we have found the critical Reynolds number depending on the number of dimples and their location.