Coil device and power conversion device

A coil device having one or more coil units, wherein

• the one or more coil units include
• a core having one or more loop-shaped magnetic paths, and
• a first winding part wound around the core so as to pass through an inner region of the core surrounded by the core,
• a metal base substrate in which a coil pattern is formed with an insulating layer interposed on a metal base body is disposed in the inner region of the core and an outer region of the core,
• a first through hole through which the core passes is formed in the metal base substrate,
• the metal base substrate is disposed to surround the core from the inner region and the outer region of the core in such a manner that a slit that divides the core so as not to continuously surround the core is formed,
• the slit is formed so as to be connected to the first through hole,
• and
• the first winding part includes the coil pattern.