A box cutter comprising: a blade slide and a blade received in the blade slide, two resilient members connected to two sides of the blade slide respectively; a pivotal member pivotably connected to a rear end of the blade slide and a first hook collected to a front end of the pivotal member, wherein an inclined face is defined in one of the surfaces of the pivotal member, wherein the inclined face being gradually raised from the front end toward a rear end of the pivotal member, wherein the inclined face is connected to a flat pressing area which has two respective rounded guide portions on two sides thereof, and wherein the rear end of the pivotal member has a push portion which is perpendicularly connected to the pressing area; a housing having a slide portion and the blade slide slidably connected to the slide portion, a second hook connected to a rear end of the housing; a cover connected to the housing and covering up an interior of the housing; a first spring connected between the first and second hooks (35, 44) and maintaining the blade slide at an initial position and maintaining the pivotal member inclined relative to the cover; a button slidably connected to outside of the cover and having a block extending from an underside thereof, wherein the block extends through an elongate hole and is inserted into the housing, wherein a second spring is connected between the button and the cover to maintain the button at an initial position where the block contacts the push portion of the pivotal member, and wherein the button is moved to move the blade slide from the initial position thereof to an extended position; and the cover having two pressing members on two sides of an underside of the cover and each of the pressing members having a slide face which is shaped to match with the guide portion of the pivotal member, and when the blade slide is located at the extended position, the pivotal member is located between the two pressing members. a blade slide and a blade received in the blade slide, two resilient members connected to two sides of the blade slide respectively; a pivotal member pivotably connected to a rear end of the blade slide and a first hook collected to a front end of the pivotal member, wherein an inclined face is defined in one of the surfaces of the pivotal member, wherein the inclined face being gradually raised from the front end toward a rear end of the pivotal member, wherein the inclined face is connected to a flat pressing area which has two respective rounded guide portions on two sides thereof, and wherein the rear end of the pivotal member has a push portion which is perpendicularly connected to the pressing area; a housing having a slide portion and the blade slide slidably connected to the slide portion, a second hook connected to a rear end of the housing; a cover connected to the housing and covering up an interior of the housing; a first spring connected between the first and second hooks (35, 44) and maintaining the blade slide at an initial position and maintaining the pivotal member inclined relative to the cover; a button slidably connected to outside of the cover and having a block extending from an underside thereof, wherein the block extends through an elongate hole and is inserted into the housing, wherein a second spring is connected between the button and the cover to maintain the button at an initial position where the block contacts the push portion of the pivotal member, and wherein the button is moved to move the blade slide from the initial position thereof to an extended position; and the cover having two pressing members on two sides of an underside of the cover and each of the pressing members having a slide face which is shaped to match with the guide portion of the pivotal member, and when the blade slide is located at the extended position, the pivotal member is located between the two pressing members.