An electromagnetic wave detection device for measuring terahertz waves comprising: a light source configured to output probe light pulses; a beam diameter changing optical system configured to change a beam diameter of the probe light pulses output from the light source ; a pulse front tilting unit configured to tilt a pulse front of the probe light pulses output from the beam diameter changing optical system ; a beam diameter adjusting optical system configured to adjust a beam diameter of the probe light pulses output from the pulse front tilting unit ; an optical effect unit configured to be input with the probe light pulses output from the beam diameter adjusting optical system and to be input with an electromagnetic wave being an object to be detected, wherein optical characteristics of the optical effect unit change due to propagation of the electromagnetic wave, and wherein the optical effect unit is configured to output the probe light pulses affected by the change in optical characteristics; and a photodetector configured to detect an intensity distribution of the probe light pulses output from the optical effect unit ; wherein the beam diameter changing optical system , the beam diameter adjusting optical system and the pulse front tilting unit are configured such that each of the measurement time range and interaction area by the probe light pulses in the optical effect unit is adjusted through a ratio of enlargement or reduction in the beam diameter of the probe light pulses by each of the beam diameter changing optical system and the beam diameter adjusting optical system and a tilt of the pulse front of the probe light pulses by the pulse front tilting unit ; and wherein the electromagnetic wave is a terahertz wave. a light source configured to output probe light pulses; a beam diameter changing optical system configured to change a beam diameter of the probe light pulses output from the light source ; a pulse front tilting unit configured to tilt a pulse front of the probe light pulses output from the beam diameter changing optical system ; a beam diameter adjusting optical system configured to adjust a beam diameter of the probe light pulses output from the pulse front tilting unit ; an optical effect unit configured to be input with the probe light pulses output from the beam diameter adjusting optical system and to be input with an electromagnetic wave being an object to be detected, wherein optical characteristics of the optical effect unit change due to propagation of the electromagnetic wave, and wherein the optical effect unit is configured to output the probe light pulses affected by the change in optical characteristics; and a photodetector configured to detect an intensity distribution of the probe light pulses output from the optical effect unit ; wherein the beam diameter changing optical system , the beam diameter adjusting optical system and the pulse front tilting unit are configured such that each of the measurement time range and interaction area by the probe light pulses in the optical effect unit is adjusted through a ratio of enlargement or reduction in the beam diameter of the probe light pulses by each of the beam diameter changing optical system and the beam diameter adjusting optical system and a tilt of the pulse front of the probe light pulses by the pulse front tilting unit ; and wherein the electromagnetic wave is a terahertz wave. <EOS>