A utility knife comprises a hollow casing formed by a pair of elongated members pivotally mounted one to the other at one end of the casing. A blade passage is provided at another end of the casing. The elongated members are adapted for movement in substantially parallel planes between aligned closed functional and open diverging positions. The casing is provided with a mechanism adapted to carry and selectively position a blade. The utility knife further comprises a locking member pivotally mounted to one of the elongated members and adapted in a closed position thereof to secure the elongated members in their aligned closed position. A pin extending inwardly from one of the side arms of the locking member is adapted to cooperate with a camming surface provided on the other one of the elongated members in order that, upon rotational movement of the locking member away from the closed position thereof, the elongated members are forcedly divergingly pivoted one with respect to the other about the other end of the casing and away from the aligned closed position thereof. As the spreading of the elongated members has been initiated by the pivot of the locking member the manual spreading of the elongated members towards the full open diverging blade removal and replacement position thereof is facilitated as well as reduced. The elongated members interlock at the blade passage to prevent the lateral spreading of the casing during use.
