Coil device and power conversion device

A coil device comprising:

• a core group including a plurality of cores forming a plurality of closed magnetic circuits;
• and
• a winding group including a plurality of winding layers formed by winding conductor wires into a tubular shape, wherein
• each of the winding layers penetrates through the closed magnetic circuits,
• when viewed from a first direction, the cores are disposed side by side with spacing along the conductor wires through which current flows,
• the cores include a first core and a second core disposed adjacent to the first core,
• a core air path is formed in a gap between the first core and the second core,
• when viewed from the first direction, the winding layers are disposed side by side with spacing along a direction intersecting a direction of the current,
• the winding layers include a first winding layer and a second winding layer disposed adjacent to the first winding layer,
• a winding air path is formed in a gap between the first winding layer and the second winding layer,
• the core group includes a first core group and a second core group each constituted with the cores, and the first core group and the second core group are adjacent to each other,
• when viewed from the first direction, the first core group and the second core group are arranged in parallel with spacing from each other,
• an inter-core-group ventilation path is formed in a gap between the first core group and the second core group adjacent to the first core group, and
• the core air path communicates with the inter-core-group ventilation surface.