A flexible Printed Circuit (PC) board, junction method thereof and battery pack using the flexible PC board prevents cracking of terminal units of a flexible PC board and reducing degradation thereof due to deformation by increasing its tensile strength. The flexible PC board has a multi-layered structure including wiring with terminal units, a first insulating layer and a second insulating layer arranged both over and under the wiring. An end of the second insulating layer is arranged between an end of the terminal units and an end of the first insulating layer.