NOVELTY - The device i.e. coreless motor (10), has permanent magnets (200) placed on a first member. An air-cored electromagnetic coil (100A) is placed on a second member. A coil back yoke (115) with a stacked structure is placed on the second member, where the electromagnetic coil is placed between the magnet and the back yoke. The electromagnetic coil includes an active coil region in which force moving the first member relatively along movement direction is generated in the electromagnetic coil, and coil end regions. The coil back yoke covers the coil region and does not cover the coil end regions.    USE - Coreless electro mechanical device i.e. coreless motor, for use as a fan motor of a digital display device, an on-vehicle device, and a device using a fuel cell e.g. fuel cell type personal computer, fuel cell type digital camera, fuel cell type video camera, fuel cell type portable telephone and projector, a needle drive motor of a timepiece, a single rotation motor of a drum type washing machine, a roller coaster, a vibration motor, a motor of different household electrical appliances and electronic devices, a spindle motor of an optical storage device, a magnetic storage device and a polygon mirror drive device and a motor for a movable body, electric bicycle, a railcar and a robot.    ADVANTAGE - The device has an arrangement that provides large torque to the device, and curbs an occurrence of distortion or saturation of output of a magnetic sensor when high torque occurs, thus reducing loss due to eddy-current loss and realizing large torque, and hence improving efficiency of the device. The active coil region is a projection region when the permanent magnet is projected toward the electromagnetic coil from the permanent magnet, so that the device utilizes magnetic flux of the permanent magnets in an effective manner, thus reducing loss and realizing large torque, and hence improving efficiency of the device. The coil back yoke has stacked steel plate materials having layered structure parallel to movement direction of a movable body, so that the device curbs generation of eddy current along direction perpendicular to the movement direction.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a coreless motor.    Coreless motor (10)    Air-cored electromagnetic coils (100A, 100B)    Cylindrically shaped portion (111)    Coil back yoke (115)    Attachment screws (120)    Permanent magnets (200)    Rotating shaft (230)