To provide factor X mutants and to provide use thereof in the treatment of blood coagulation disorder.SOLUTION : Disclosed is a protein which is a factor X comprising at least one mutation A, A' , B, C or C' , the mutation A consisting of substituting amino acids 43 to 52, the mutation A' consisting of substituting amino acids 47 to 52, the mutation B consisting of inserting a sequence into between amino acids 52 and 53, the mutation C consisting of inserting a sequence into between amino acids 52 and 53 as well as deleting amino acids 4 to 13, and the mutation C' consisting of inserting a sequence into between amino acids 52 and 53 as well as deleting amino acids 4 to 9.SELECTED DRAWING : None