Utility knife

A utility knife, comprising:

• a handle having a first casing and a second casing coupled, a chamber between the first and second casings, an elongated slot at a top thereof communicated with the chamber and an opening at a front end thereof communicated with the chamber;
• a blade holder slidably received in the chamber of the handle and having a supporting portion at where a blade is attached, at least one flange projected from the supporting portion to be against the blade, an arm projected from the supporting portion and a button at a distal end of the arm and extended out of the handle via the slot, wherein the blade has at least a recess at a top thereof and the supporting portion of the blade holder has an elastic piece with a lock portion at a distal end thereof to be engaged with the recess of the blade and a pushing portion at a top of the lock portion;
• and
• means for pressing the elastic piece of the blade holder to disassemble the blade from the blade holder;
• wherein the second casing has a blade room at where relates to the blade holder to receive reserved blades therein, an elastic member in the blade room to push the reserved blades toward the blade holder and a post to push the pushing portion of the elastic piece of the blade holder.