A mask, comprising: a main body; a mask cord connected to the main body; and a cord lock attached to the mask cord; the cord lock and the mask cord together with the main body forming a circle contour for putting on a user's head to fix the main body to the user's face; and the cord lock being made of an elastic material to be movable relatively with the mask cord; and characterized in that the cord lock includes: a locking portion provided with a bore extended in a cord insertion direction; and the bore being elastically expandable by the mask cord, so that the mask cord is clamped by the locking portion; and a grip portion having an annular wall connected to the locking portion; the annular wall internally defining a receiving space communicable with the bore of the locking portion; and the mask cord having a confined section (221, 222) including two bilaterally symmetrical parts being received in the bore and the receiving space; the annular wall of the grip portion including a deformable zone and a supporting zone having a wall thickness larger than the wall thickness of the deformable zone; the locking portion, the deformable zone and the supporting zone are arranged in a straight line from bottom to top without overlapping one another in an initial state; the deformable zone being bendable to form a first bent part and a second bent part when the cord lock is subjected to a force from a direction parallel to the cord insertion direction; and the deformable zone is caused to overlap the locking portion, such that the cord lock is changed from the initial state into a invagination state; and wherein when the cord lock is changed from the initial state into the invagination state, or changed from the invagination state into the initial state, a size of the circle contour is changed accordingly. a main body; a mask cord connected to the main body; and a cord lock attached to the mask cord; the cord lock and the mask cord together with the main body forming a circle contour for putting on a user's head to fix the main body to the user's face; and the cord lock being made of an elastic material to be movable relatively with the mask cord; and characterized in that the cord lock includes: a locking portion provided with a bore extended in a cord insertion direction; and the bore being elastically expandable by the mask cord, so that the mask cord is clamped by the locking portion; and a grip portion having an annular wall connected to the locking portion; the annular wall internally defining a receiving space communicable with the bore of the locking portion; and the mask cord having a confined section (221, 222) including two bilaterally symmetrical parts being received in the bore and the receiving space; the annular wall of the grip portion including a deformable zone and a supporting zone having a wall thickness larger than the wall thickness of the deformable zone; the locking portion, the deformable zone and the supporting zone are arranged in a straight line from bottom to top without overlapping one another in an initial state; the deformable zone being bendable to form a first bent part and a second bent part when the cord lock is subjected to a force from a direction parallel to the cord insertion direction; and the deformable zone is caused to overlap the locking portion, such that the cord lock is changed from the initial state into a invagination state; and wherein when the cord lock is changed from the initial state into the invagination state, or changed from the invagination state into the initial state, a size of the circle contour is changed accordingly. a locking portion provided with a bore extended in a cord insertion direction; and the bore being elastically expandable by the mask cord, so that the mask cord is clamped by the locking portion; and a grip portion having an annular wall connected to the locking portion; the annular wall internally defining a receiving space communicable with the bore of the locking portion; and the mask cord having a confined section (221, 222) including two bilaterally symmetrical parts being received in the bore and the receiving space; the annular wall of the grip portion including a deformable zone and a supporting zone having a wall thickness larger than the wall thickness of the deformable zone; the locking portion, the deformable zone and the supporting zone are arranged in a straight line from bottom to top without overlapping one another in an initial state; the deformable zone being bendable to form a first bent part and a second bent part when the cord lock is subjected to a force from a direction parallel to the cord insertion direction; and the deformable zone is caused to overlap the locking portion, such that the cord lock is changed from the initial state into a invagination state; and wherein when the cord lock is changed from the initial state into the invagination state, or changed from the invagination state into the initial state, a size of the circle contour is changed accordingly.