The operation of the electrodynamic human motion energy harvester with flat structure is under investigation. Electrodynamic harvester consists of a flat, spiral-shaped coil and a rectangular magnet. All parts of the harvester can be deployed both on a variety of clothing items which move one relative to another during the human motion. During the process of human motion magnet is moved along the coil and induced the pulses of voltage. By optimization of coil and magnet dimensions the mean power of into the jacket integrated prototype about 0,2 mW is obtained. With the planar coil geometry the generator's minimal volume and occupied space are achieved, therefore power density of generator (about 1,82 mW/cm3) is higher than proposed by other researchers and it is suitable to be fully integrated into clothing.