A Selective Catalytic Reduction (SCR) catalytic converter that does not require the injection of a reducing agent, and, particularly, to an open-flow type or wall-flow type SCR catalytic converter that does not require the injection of a reducing agent, which includes a front portion, in which first supports supporting modified catalyst components are applied on the inner surfaces of porous partition walls, a middle portion, in which second supports supporting ammonia synthesis catalyst components are applied on the inner surfaces of porous partition walls, and a rear portion, in which third supports supporting SCR reducing catalyst components are applied on the inner surfaces of porous partition walls. The catalytic converter can improve a reduction rate of NOx without requiring the injection of an ammonia reducing agent from the outside.