For achieving an expanded observation range without sacrificing resolution, a scanning optical system according to the present invention includes a scanner that deflects laser light from a light source while changing a deflection angle of the laser light; a polarization beam splitter that is capable of splitting-off the laser light from an optical path of the laser light deflected by the scanner; a polarization beam splitter that is disposed between the light source and the scanner and that causes the laser light split-off by the polarization beam splitter to travel toward the scanner; and a first relay optical system that has 1× relay magnifying power and that is disposed between the polarization beam splitter and the polarization beam splitter. The first relay optical system relays the laser light split-off by the polarization beam splitter so as to cause the laser light to be incident again on the scanner at the same position as an incident position of the laser light from the light source via the polarization beam splitter.