1. A moving picture coding method of coding a current block which is included in a current picture by performing temporal prediction using a co-located block which is included in a coded picture, the co-located block having two reference motion vectors, the two reference motion vectors being two motion vectors calculated with reference to one or more pictures located before the current picture in display order, said moving picture coding method comprising: coding the current block using a first motion vector and a second motion vector, respectively, with reference to a first reference picture list and a second reference picture list; generating a first predictive motion vector and a second predictive motion vector; and coding the first motion vector and the second motion vector, respectively, using the first predictive motion vector and the second predictive motion vector, wherein (i) when any reference pictures in the first reference picture list and the second reference picture list are located before the current picture in display order, the first predictive motion vector is generated using a first reference motion vector out of the two reference motion vectors, the first predictive motion vector and the first reference motion vector each corresponding to the first reference picture list, and the second predictive motion vector is generated using a second reference motion vector out of the two reference motion vectors, the second predictive motion vector and the second reference motion vector each corresponding to the second reference picture list, the second reference motion vector being different than the first reference motion vector, and (ii) when a reference picture in the first reference picture list and the second reference picture list are not located before the current picture in display order, and the first reference motion vector and the second reference motion vector refer to different directions, both of the first predictive motion vector and the second predictive motion vector are generated using only one of the first reference motion vector and the second reference motion vector.