<;P>;PROBLEM TO BE SOLVED: To provide a protein kinase inhibitor not conventionary elucidated, a method for producing the same, a medicinal composition for treating cancer and a reagent. <;P>;SOLUTION: This protein kinase inhibitor and the medicinal composition for treating the cancer contains violacein expressed by formula as an active ingredient. The violacein can be obtained by inoculating ocean bacteria of Pseudoalteromonas sp. strain, culturing, recovering a cultured bacterium together with the violacein, separating it from the recovered material, concentrating and purifying. <;P>;COPYRIGHT: (C)2010,JPO&INPIT