© 2017 Optical Society of America. In the generation of Schrödinger’s cat states using an optical parametric oscillator in the continuous-wave regime up until now, single photons are subtracted from the whole bandwidth of the squeezed vacua. However, it was pointed out recently that the achievable purities are limited in such method [J. Yoshikawa, W. Asavanant, and A. Furusawa, Phys. Rev. A 96, 052304 (2017)]. In this paper, we used our new photon subtraction method with a narrowband filtering cavity and generated a highly pure Schrödinger’s cat state with the value of −0.184 ± 0.001 at the origin of the Wigner function. To our knowledge, this is the highest value ever reported without any loss corrections. The temporal mode also becomes exponentially rising in our method, which we utilize to make a real-time quadrature measurement on Schrödinger’s cat states, and we obtained the value of −0.162 ± 0.001 at the origin of the Wigner function.