the power driver 103 may be controlled on the basis of the positional relationship between magnetic poles on the movable member and magnetic poles on the stator estimated in the controller 102 from the induced voltage e 0 calculated from a voltage and a measured electric current supplied to the linear motor 101 as shown in fig4 a relative movement between the first and second members may be brought about by a pair of the linear motors 101 as shown in fig5 the linear motors 101 may be selectively connected to one of the elastic members 107 a and 107 b to drive the second member 110 in either direction as shown in fig6 a and 6 b a first magnetic core 51 forms a first pair of magnetic poles 11 a and 21 b and a second magnetic core 52 forms a second pair of magnetic poles 12 b and 22 a a 2n u2212 1 th magnetic core has the first pair of magnetic poles 11 a and 21 b and a 2n th magnetic core has the second pair of magnetic poles 12 b and 22 a when n 1 2 3 the first magnetic core 51 and second magnetic core 52 are surrounded by a single electromagnetic coil 4 a movable member 6 including pairs of magnetic poles whose pitch pm is equal to a pitch ps between the first magnetic cores 51 and 52 adjacent to each other in a movable direction of the movable member 6 is movable in a gap 8 between the magnetic poles 11 a and 21 b of the first magnetic.