There is to provide a coil part capable of reducing the number of fastening means such as screws and so on required when attaching it to a substrate. A coil part includes a transformer unit and a reactor unit, wherein the transformer unit includes: a primary winding part formed by winding a flat wire around a primary side hollow part; secondary winding parts, the secondary winding part being formed by winding a flat wire around a secondary side hollow part communicating with the primary side hollow part, arranged in pairs in a state of facing one side and another side of the primary winding part respectively; and a first core inserted into the primary side hollow part and the secondary side hollow part, and the reactor unit includes: a reactor winding part formed by extending one terminal side of the flat wire constituting the secondary winding part and winding the flat wire around a reactor side hollow part; and a second core inserted into the reactor side hollow part.