(57) A protective helmet which a driver wears in driving a vehicle which comprises; a helmet body having a front opening; and a windshield plate detachably coupled to the helmet body in such a manner as to close and open the front opening of the helmet, CHARACTERIZED by comprising: a pair of locking substrates (8) secured to the helmet body at both sides thereof, a pair of windshield plate locking elements (12) is provided on both sides, and a pair of windshield plate cover members (19) provided on both sides. Each locking substrate (8) includes a first annular axis portion (2) and a second annular axis portion (4) provided outside the first annular axis portion (2) so that the second annular axis portion (4) is coaxial with the first annular axis portion (2), and elastic pawls (6 and 7) formed above and below the axis portions which are bendable to lock or unlock the windshield plate (5). Each windshield plate locking element (12) including an annular rotary axis portion (9) rotatably put on the first annular axis portion (2), a cut (10) formed in the outer periphery of the annular rotary axis portion (9), and a lever (11) extended from the outer periphery of the annular rotary axis portion (9). Each windshield plate cover member (19) is detachably engaged with the locking section of the windshield plate (5) and the windshield plate locking element (12) with the locking substrate (8) from above.