Disclosed is a flexible circuit board having a three-layer dielectric body and four-layer ground layer structure. A flexible circuit board having a three-layer dielectric body and four-layer ground layer structure, according to the present invention, comprises: a first dielectric body; a second dielectric body facing the flat surface of the first dielectric body; a third dielectric body facing the bottom side of the first dielectric body; a signal line formed on the flat surface of the first dielectric body; a pair of first ground layers laminated on the flat surface of the first dielectric body and having the signal line therebetween; second ground layers laminated on the bottom side of the first dielectric body so as to correspond to the first ground layers; a third ground layer laminated on the flat surface of the second dielectric body; and a fourth ground layer laminated on the bottom side of the third dielectric body.