Coil device

A coil device comprising:

• a main core including a middle leg for winding a coil body and an outer leg connected with the middle leg via a base portion;
• and
• a sub core disposed to face the base portion across the middle leg,
• wherein the main core has a relative permeability of 15-100,
• a gap between the middle leg and the sub core is wider than that between the outer leg and the sub core,
• the sub core is fixed to the main core with an adhesive agent disposed on a top surface of the middle leg,
• no adhesive agent exists between the outer leg and the sub core,
• the gap between the middle leg and the sub core has a width of 15 to 55 μm, wherein the gap between the middle leg and the sub core is located around the adhesive agent,
• the coil body is made of a plate conductor and wound around the middle leg by less than one turn, and
• a height from a bottom surface of a recess, formed on the main core for accommodating the coil body, to the top surface of the middle leg is smaller than a height from the bottom surface of the recess to a top surface of the outer leg.