A coil device, in which an air-core coil of a cylindrical shape is buried in a core including a magnetic powder and a resin, showing, CV value of the below described cross sectional areas, SA1 to SA5, 0.55 or less, when an outer diameter of the air-core coil is “a1”, an inner diameter of the same is “a2”, and a distance between a surface of the core perpendicular to a direction of winding axis and an end of the air-core coil in the direction of winding axis is “h”, is provided. The coil device is superior in DC superimposing characteristic while suppressing the magnetic saturation.