Scanning optical system and light projection and reception device

Provided are a scanning optical system and a radar which are capable of achieving reflected light of sufficient intensity on a wide-ranging object to be measured. The present invention causes luminous flux, emitted from light sources, to be reflected twice by a first mirror surface and a second mirror surface and therefore enables light projection in which variations in rotation angles of spot lights do not readily occur in a scanning range. Consequently, a state can be maintained in which the plurality of spot lights reflected by the second mirror surface are aligned along a direction intersecting the main scanning direction at the object side regardless of the position in the main scanning direction, and light can therefore be projected, with one scan, onto the wide-ranging object while suppressing measurement omissions.