We study experimentally a vacuum induced Aulter-Townes doublet in a superconducting three-level artificial atom strongly coupled to a coplanar waveguide resonator and simultaneouslyto a transmission line. The Aulter-Townes splitting is observed in the reflection spectrum of the three-level atom when the transition between two excited states is resonant with the resonator. By varying an amplitude of the driving field applied to the resonator, we observe quantum-to-classical transition of the Aulter-Townes splitting. Our results may pave the way for the control of microwaves by single photons.