Spectroscopy is the “eyes” of modern science, and hence it plays essential roles in a variety of research fields covering physics, chemistry, and biology. We develop and utilize the most advanced spectroscopy for molecular science of complex systems in the condensed phase. To elucidate a variety of complex phenomena occurring in the condensed phase, we need to clarify the electronic and vibrational states of molecules, the response of surroundings, and the fluctuation and dissipation of energy behind. Based on this view, we carry our fundamental research using the most advanced linear/nonlinear spectroscopic methods with most suitable time- and space-resolution for the problems to be studied.