An apparatus visualizing internal information of an object includes a detection unit of terahertz wave, a generating unit of a time waveform of the terahertz wave, a modulation unit, an adjustment unit, and an addition unit. The modulation unit sequentially performs spatial modulation on a propagation distance for each pixel of a terahertz wave corresponding to a pixel in a horizontal direction by using a plurality of modulation patterns, and emits a plurality of terahertz waves. Based on a time amount converted from the change of the propagation distances corresponding to the modulation patterns, the adjustment unit adjusts a position on a time axis of the time waveforms of a plurality of terahertz waves and calculates a new plurality of time waveforms. The addition unit adds a new time waveform for each pixel. The apparatus can suppress reduction in signal intensity of a terahertz wave while maintaining detection sensitivity.