This paper describes a newly developed plane magnetic-abrasive finishing apparatus and its finishing performance using magnetic-abrasives made of both iron and alumina particles in magnetic field. The process principle and the construction of the finishing apparatus are explained in detail respectively for applicating magnetic-abrasive finishing process to plane workpiece, and the calculating method is also described on magnetic circuit needed to design the finishing apparatus. The finishing performance obtained by the experiments shows that the prefinished surface roughness value of 1.3 μmR_max (material ; SUS 304 stainless steel, thickness ; 1.2 mm, finished area ; 44 cm²) is improved to 0.15 μmR_max in two minutes finishing time.