A rotating body non-contact power-feeding device, comprising: a power receiving-side substrate with a power receiving-side circuit component mounted thereat, which is fixed to a rotating shaft supported via a bearing and rotates as one with the rotating shaft; and a power transmitting-side substrate with a power transmitting-side circuit component mounted thereat, which is fixed to a holding unit holding the bearing so that a substrate surface thereof faces opposite a substrate surface of the power receiving-side substrate and is connected with a power source, wherein: a power transmitting-side coil (310a, 310b) is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with a plurality of turns at a substrate surface facing opposite the power receiving-side substrate and the power transmitting-side circuit component is mounted at another substrate surface, at the power transmitting-side substrate that includes a substrate front surface and a substrate back surface, a power receiving-side coil is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with at least one turn at a substrate surface facing opposite the power transmitting-side substrate and the power receiving-side circuit component is mounted at another substrate surface, at the power receiving-side substrate that includes a substrate front surface and a substrate back surface; the power transmitting-side coil (310a, 310b) and the power receiving-side coil are magnetically coupled with each other so as to allow power to be contactlessly fed from the power transmitting-side substrate to the power receiving-side substrate; wherein: a gap between adjacent pattern line portions is set greater than a pattern line width in the conductive pattern at the power transmitting-side coil (310a, 310b); and the power receiving-side coil assumes a plurality of turns and a gap between adjacent pattern line portions is set greater than a pattern line width at the power receiving-side coil. a power receiving-side substrate with a power receiving-side circuit component mounted thereat, which is fixed to a rotating shaft supported via a bearing and rotates as one with the rotating shaft; and a power transmitting-side substrate with a power transmitting-side circuit component mounted thereat, which is fixed to a holding unit holding the bearing so that a substrate surface thereof faces opposite a substrate surface of the power receiving-side substrate and is connected with a power source, wherein: a power transmitting-side coil (310a, 310b) is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with a plurality of turns at a substrate surface facing opposite the power receiving-side substrate and the power transmitting-side circuit component is mounted at another substrate surface, at the power transmitting-side substrate that includes a substrate front surface and a substrate back surface, a power receiving-side coil is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with at least one turn at a substrate surface facing opposite the power transmitting-side substrate and the power receiving-side circuit component is mounted at another substrate surface, at the power receiving-side substrate that includes a substrate front surface and a substrate back surface; the power transmitting-side coil (310a, 310b) and the power receiving-side coil are magnetically coupled with each other so as to allow power to be contactlessly fed from the power transmitting-side substrate to the power receiving-side substrate; wherein: a gap between adjacent pattern line portions is set greater than a pattern line width in the conductive pattern at the power transmitting-side coil (310a, 310b); and the power receiving-side coil assumes a plurality of turns and a gap between adjacent pattern line portions is set greater than a pattern line width at the power receiving-side coil. a power transmitting-side coil (310a, 310b) is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with a plurality of turns at a substrate surface facing opposite the power receiving-side substrate and the power transmitting-side circuit component is mounted at another substrate surface, at the power transmitting-side substrate that includes a substrate front surface and a substrate back surface, a power receiving-side coil is formed with a conductive pattern so as to achieve a flat-plane spiral pattern with at least one turn at a substrate surface facing opposite the power transmitting-side substrate and the power receiving-side circuit component is mounted at another substrate surface, at the power receiving-side substrate that includes a substrate front surface and a substrate back surface; the power transmitting-side coil (310a, 310b) and the power receiving-side coil are magnetically coupled with each other so as to allow power to be contactlessly fed from the power transmitting-side substrate to the power receiving-side substrate; wherein: a gap between adjacent pattern line portions is set greater than a pattern line width in the conductive pattern at the power transmitting-side coil (310a, 310b); and the power receiving-side coil assumes a plurality of turns and a gap between adjacent pattern line portions is set greater than a pattern line width at the power receiving-side coil.