A system conversion apparatus and method for image signals are disclosed, in which an interlaced scanning image signal S1 is converted into a progressive scanning image signal S2 by an IP converter (1), a block-based motion vector is searched for based on the progressive scanning image signal S2 by a block-based motion vector search unit (5), a motion vector with minimum motion estimation error determined for each mini-block using the block-based motion vector is assigned as a pixel-based motion vector in a mini-block by a pixel-based motion vector generator (6), and an interpolated frame of the image signal is generated using the pixel-based motion vector and a progressive scanning image signal sequence S4 higher in frame frequency is output by a motion compensative interpolated frame generator (7).