Safety protection helmet

The utility model relates to a safety protection helmet, it includes the cap body, and a head circumference adjusting device is established to the inside circle of this cap body, and the outside of this cap body is equipped with a rotatory adjustment button, and the one end of this rotation adjustment button is equipped with the driving piece, combine an apron on this cap body, this apron has first block portion and can supply to fix a position the locating hole of this rotation adjustment button, one side of this apron joins a fastener, and this fastener is equipped with interlock portion and second block portion, and wherein, this interlock portion joins this driving piece, this first block portion of second block portion joint, and an elastic component joins this fastener, and by this, when pressing rotatory adjustment button with elasticity of compression spare, when making second block portion be disjuncture with first block portion, can make rotatory adjustment button and the fastener is synchronous rotates, adjustment head circumference adjusting device's elasticity to the head circumference size that is fit for the user.