First to third interpolation processing circuits 20a, 20b and 20c are configured by a data identifying unit 51, a data converting unit 52, a data interpolating unit 53, a data reconverting unit 54 and four switches SW1 to SW4. After the data identifying unit 51 determines a value of velocity data, the data converting unit 52, the data interpolating unit 53 and the data reconverting unit 54 switch between vector operation on a complex space based on a scalar array and vector operation on a complex space based on a color palette array and execute interpolation processing.
