A base station apparatus in a radio communications system is disclosed. The radio communications system has a mobile station apparatus and the base station apparatus in communication with the mobile station apparatus to which is applied a scheduling scheme which allocates a radio resource for each of constant periods. The base station apparatus includes a first transmitting unit which conducts a first transmission of a first signal for each of the constant periods based on the scheduling scheme; and a second transmitting unit which conducts second and subsequent transmissions at predetermined timings when an error occurs in the first transmission.