The present invention provides a polarization switching liquid crystal element 1 having TN liquid crystal 7 retained between two transparent substrates 2a and 2b for transmitting at least visible polarized light with the polarized light transmission axis selectively rotated by 90 degrees when a voltage is selectively applied to the TN liquid crystal 7, wherein a phase difference u of said TN liquid crystal 7 is defined by the following equation: u=2×Δn×d/λ, where Δn is the refractive index anisotropy of said TN liquid crystal 7, d is the thickness of said TN liquid crystal 7, and λ is the wavelength of said polarized light, and a transmittance T of said polarization switching liquid crystal element measured with polarization plates on the incident and outgoing sides is defined by the following equation: T=(½)×sin2{π(1+u2)1/2/2}/(1+u2), and wherein the phase difference u includes a value 1.7 and the transmittance T is 0.1 or lower when the λ ranges from 400 nm to 700 nm. Then, a polarization switching liquid crystal element having a high response speed and reduced wavelength-dependency can be realized using inexpensive and highly durable TN liquid crystal without increasing parts cost.