1. An apparatus for visualizing subsurface structure using waveform inversion in the Laplace-Fourier domain, the apparatus comprising a receiver receiving a seismic signal from a target region that is to be measured, and a signal processor processing the seismic signal to generate image data for visualizing the subsurface velocity structure of the target region, wherein the signal processor comprises: an input unit receiving time-domain measured data from the receiver; a transformer transforming the time-domain measured data into Laplace-Fourier-domain measured data using a complex damping constant; a modeled data generator setting up an equation including parameters representing physical characteristics and solving the equation in the Laplace-Fourier domain to obtain modeled data; and a parameter update unit updating the parameters by comparing the Laplace-Fourier-domain measured data with the modeled data.