An absorbent article for a pet, comprising: a liquid permeable top surface layer; a liquid impermeable back surface layer; and an absorbent core positioned between the top surface layer and the back surface layer; wherein the absorbent article for a pet is configured in a rectangular shape having a first end portion and a second end portion opposed to each other, and a pair of side portions opposed to each other and orthogonal to the first end portion and the second end portion, and wherein, in a state of being wrapped around a pet's waist, the first end portion is arranged on a side to the pet's body, and the second end portion is removably attached to an outer surface of the first end portion, the absorbent article for a pet further comprising: a locking member being arranged on an outer surface side of the first end portion, and being capable of locking an inner surface of the second end portion, characterized in that: at least a part of an outer surface of the back surface layer is constituted of a member that can be locked by the locking member, the first end portion is configured by extending the top surface layer and the back surface layer from an edge of the absorbent core, a low rigidity area is formed in the first end portion, on the second end portion side of the portion in which the locking member is arranged, rigidity of the low rigidity area being lower than that of the portion in which the locking member is arranged, the low rigidity area is constituted of a portion in which the top surface layer and the back surface layer are extended from the edge of the absorbent core, and the length of the low rigidity area along a longitudinal direction of the absorbent article for a pet is greater than the length of the locking member along the longitudinal direction of the absorbent article for a pet. the absorbent article for a pet further comprising: a locking member being arranged on an outer surface side of the first end portion, and being capable of locking an inner surface of the second end portion, characterized in that: at least a part of an outer surface of the back surface layer is constituted of a member that can be locked by the locking member, the first end portion is configured by extending the top surface layer and the back surface layer from an edge of the absorbent core, a low rigidity area is formed in the first end portion, on the second end portion side of the portion in which the locking member is arranged, rigidity of the low rigidity area being lower than that of the portion in which the locking member is arranged, the low rigidity area is constituted of a portion in which the top surface layer and the back surface layer are extended from the edge of the absorbent core, and the length of the low rigidity area along a longitudinal direction of the absorbent article for a pet is greater than the length of the locking member along the longitudinal direction of the absorbent article for a pet. a locking member being arranged on an outer surface side of the first end portion, and being capable of locking an inner surface of the second end portion, characterized in that: at least a part of an outer surface of the back surface layer is constituted of a member that can be locked by the locking member, the first end portion is configured by extending the top surface layer and the back surface layer from an edge of the absorbent core, a low rigidity area is formed in the first end portion, on the second end portion side of the portion in which the locking member is arranged, rigidity of the low rigidity area being lower than that of the portion in which the locking member is arranged, the low rigidity area is constituted of a portion in which the top surface layer and the back surface layer are extended from the edge of the absorbent core, and the length of the low rigidity area along a longitudinal direction of the absorbent article for a pet is greater than the length of the locking member along the longitudinal direction of the absorbent article for a pet. at least a part of an outer surface of the back surface layer is constituted of a member that can be locked by the locking member, the first end portion is configured by extending the top surface layer and the back surface layer from an edge of the absorbent core, a low rigidity area is formed in the first end portion, on the second end portion side of the portion in which the locking member is arranged, rigidity of the low rigidity area being lower than that of the portion in which the locking member is arranged, the low rigidity area is constituted of a portion in which the top surface layer and the back surface layer are extended from the edge of the absorbent core, and the length of the low rigidity area along a longitudinal direction of the absorbent article for a pet is greater than the length of the locking member along the longitudinal direction of the absorbent article for a pet.