candidate 245 if reference field and coding field are bottom and top fields respectively the condition judgment table 241 is used for outputting selection information indicating the selection of a third chrominance motion vector 246 candidate in this case the first second or third chrominance motion vector candidates 244 245 and 246 are connected to 262 shown in fig1 272 shown in fig1 and 282 shown in fig1 respectively then a selector 243 selects one of the first second and third chrominance motion vector candidates 244 245 and 246 based on the selection information 249 and outputs mvc_x mvc_y as its chrominance motion vector 242 fig2 shows the operation of the present invention to calculate a chrominance vector using a luminance vector in the case where reference field and coding field are bottom and top fields respectively in the example shown in fig2 a luminance motion vector mv_x mv_y used to predict a top coding field pixel 160 is assumed to be 0 1 in this case a reference field bottom field luminance pixel position 161 is selected for the prediction of a luminance pixel 160 the calculation process of a chrominance motion vector to be used to predict a top coding field chrominance pixel 162 is described below with reference to fig1 firstly in fig2 reference field and coding field are bottom and top fields respectively in this case the condition judgment table 241 shown in fig1 is used for selecting selection information 249 about the third chrominance motion vector candidate according to equation 11 the third chrominance motion vector candidate is calculated as follows mvc u2062 3 u2062 _ u2062 x mvc u2062 u2062 3 u2062 _ u2062.