The free vibration of a helical spring is analyzed by a finite element method. The mass and stiffness matrices including the effects of the pitch angle and the number of active coils are derived by using the exact solution of the equations of the helical spring in static equilibrium, and the natural frequencies and associated modes are estimated numerically. The effects of the pitch angle and the number of active coils on the natural frequencies are studied closely, and it is pointed out that the effects of the pitch angle, even if minor, should be taken into consideration. The obtained results are corroborated with the experimental results.