A storage container comprising: a container body for accommodating articles; a door element for opening and closing an opening of the container body; and a locking mechanism for locking the door element that covers the opening of the container body, the door element being formed of a casing to be fitted to the opening of the container body and a cover that covers the casing, the locking mechanism includes: a rotatable rotary element; a first advancing and retracting element being arranged between the casing and the cover, which, in accordance with the rotation of the rotary element, projects towards the door element's periphery from a door element's reference position when the door element is locked and returns to the door element's reference position when the door element is unlocked; a second advancing and retracting element being arranged between the casing and the cover, which is rotatably supported by the first advancing and retracting element, and projects out from the door element to be inserted into a recess in the inner periphery of the opening of the container body when the door element is locked and returns from the recess of the container body towards the door element when the door element is unlocked; and a guide element for inclining the second advancing and retracting element in the door element's direction of thickness when it is projecting, the first advancing and retracting element including a neck portion at its front end part and a coupling pin attached to said neck portion, the second advancing and retracting element being formed as an approximately flat plate, including a U-shaped grooved portion formed in its end part which detachably receives and holds the coupling pin of the first advancing and retracting element, and including pin projections projectively formed on both lateral sides thereof, characterized in that the second advancing and retracting element includes indentations and projections parallel-formed on both sides, a plurality of guides of linear rail configurations opposing each other are formed on both the opposing surfaces of the casing and the cover, the first advancing and retracting element and the second advancing and retracting element being guided along guide surfaces of the plurality of guides, the pin projections being slidably held between guides of casing and cover, and the front end part of the second advancing and retracting element is formed in a shape having a triangular section, in a wedge shape, or in an arrow shape reducing the area of contact with recess of the container body. a rotatable rotary element; a first advancing and retracting element being arranged between the casing and the cover, which, in accordance with the rotation of the rotary element, projects towards the door element's periphery from a door element's reference position when the door element is locked and returns to the door element's reference position when the door element is unlocked; a second advancing and retracting element being arranged between the casing and the cover, which is rotatably supported by the first advancing and retracting element, and projects out from the door element to be inserted into a recess in the inner periphery of the opening of the container body when the door element is locked and returns from the recess of the container body towards the door element when the door element is unlocked; and a guide element for inclining the second advancing and retracting element in the door element's direction of thickness when it is projecting, the first advancing and retracting element including a neck portion at its front end part and a coupling pin attached to said neck portion, the second advancing and retracting element being formed as an approximately flat plate, including a U-shaped grooved portion formed in its end part which detachably receives and holds the coupling pin of the first advancing and retracting element, and including pin projections projectively formed on both lateral sides thereof, characterized in that the second advancing and retracting element includes indentations and projections parallel-formed on both sides, a plurality of guides of linear rail configurations opposing each other are formed on both the opposing surfaces of the casing and the cover, the first advancing and retracting element and the second advancing and retracting element being guided along guide surfaces of the plurality of guides, the pin projections being slidably held between guides of casing and cover, and the front end part of the second advancing and retracting element is formed in a shape having a triangular section, in a wedge shape, or in an arrow shape reducing the area of contact with recess of the container body.