Spiral waves have been investigated in many different excitable media. A set of multiarmed spiral waves is a spacial self-organization and rarely studied in experiments because they are difficult to be created. We present a method to generate multiarmed spiral waves pinned to an unexcitable circular obstacle in a thin layer of the Belousov-Zhabotinsky reaction using a partition method. A thin rectangle and a thin disk made from chemically innert plastic (acrylic) are used as the partition and the obstacle, respectively. We demonstrate an initiation of three-armed spiral waves.