To provide a foldable utility knife easily folding a blade into a handle, firmly holding the blade, facilitating its replacement, being simply used, and dispensing with a high cost for the manufacture and maintenance.

This utility knife 1 is provided with a handle 2 and a blade holder 3 which is pivotally mounted on the handle for movement from an unfolded position to a folded position. The handle has a space adapted to receive the blade holder when the blade holder is in its folded position. The blade holder includes a main wall 34 and a guard wall 35 pivotally mounted on the main wall to pivot from an open position to a closed position overlying the main wall. The main wall is adapted to hold a blade so that a blade is interposed between the main wall and guard wall when the guard wall is in its closed position.