To provide a coil device for MRI system which dispenses with RF shield between a gradient magnetic field coil and an RF coil which is arranged conventionally and is favorable for high speed photographing.

This coil device is provided with a magnet 11 generating static magnetic field in a space for diagnosis, a gradient magnetic field coil 12 generating a gradient magnetic field pulse to be superimposed on the static magnetic field, and an RF coil 13 transmitting and receiving a high frequency pulse signal between an object to be examined and it. The gradient magnetic field coil 12 is constituted by an active (self) shield type gradient magnetic field coil. The RF coil 13 is disposed on an outside diameter side of the active shield type gradient magnetic field coil 12. The active shield type gradient magnetic field coil 12 is constituted in substantially transparent state with respect to a high frequency magnetic field signal. Consequently, RF signal between the RF coil 13 and the active shield type gradient magnetic field coil becomes unnecessary. The gradient magnetic filed coil 12 is favorable for high speed photographing by EPI method.