A disposable diaper for pet, comprising: a waistline direction disposed along a waistline direction of a pet; a cross direction orthogonal to the waistline direction; a main body portion having a topsheet, a backsheet, and an absorbent core arranged between the topsheet and the backsheet; and a binding portion that binds opposing parts of the main body portion when wrapped around a waist of the pet in a wearing state, the main body portion including: a main-body first end (2E1) which forms one end in the waistline direction; a main-body second end (2E2) which forms the other end in the waistline direction, and arranged an outside of the disposable diaper in the wearing state; a main-body third end (2E3) which forms one end in the cross direction, and arranged on a head-side of the pet in the wearing state; a main-body fourth end (2E4) which forms the other end in the cross direction, and arranged on a crotch-side of the pet in the wearing state; and a mark portion being designed visible from a side of the backsheet of the disposable diaper for pet, and to indicate a position of the main-body second end in the wearing state, the mark portion including: a head-side mark portion residing on a side of the main-body third end of a center in the cross direction of the main body portion; and a crotch-side mark portion residing on a side of the main-body fourth end of the center in the cross direction of the main body, characterized in that the head-side mark portion is positioned inside or outside, in the waistline direction, of the crotch-side mark portion. a waistline direction disposed along a waistline direction of a pet; a cross direction orthogonal to the waistline direction; a main body portion having a topsheet, a backsheet, and an absorbent core arranged between the topsheet and the backsheet; and a binding portion that binds opposing parts of the main body portion when wrapped around a waist of the pet in a wearing state, the main body portion including: a main-body first end (2E1) which forms one end in the waistline direction; a main-body second end (2E2) which forms the other end in the waistline direction, and arranged an outside of the disposable diaper in the wearing state; a main-body third end (2E3) which forms one end in the cross direction, and arranged on a head-side of the pet in the wearing state; a main-body fourth end (2E4) which forms the other end in the cross direction, and arranged on a crotch-side of the pet in the wearing state; and a mark portion being designed visible from a side of the backsheet of the disposable diaper for pet, and to indicate a position of the main-body second end in the wearing state, the mark portion including: a head-side mark portion residing on a side of the main-body third end of a center in the cross direction of the main body portion; and a crotch-side mark portion residing on a side of the main-body fourth end of the center in the cross direction of the main body, characterized in that the head-side mark portion is positioned inside or outside, in the waistline direction, of the crotch-side mark portion. a main-body first end (2E1) which forms one end in the waistline direction; a main-body second end (2E2) which forms the other end in the waistline direction, and arranged an outside of the disposable diaper in the wearing state; a main-body third end (2E3) which forms one end in the cross direction, and arranged on a head-side of the pet in the wearing state; a main-body fourth end (2E4) which forms the other end in the cross direction, and arranged on a crotch-side of the pet in the wearing state; and a mark portion being designed visible from a side of the backsheet of the disposable diaper for pet, and to indicate a position of the main-body second end in the wearing state, the mark portion including: a head-side mark portion residing on a side of the main-body third end of a center in the cross direction of the main body portion; and a crotch-side mark portion residing on a side of the main-body fourth end of the center in the cross direction of the main body, characterized in that the head-side mark portion is positioned inside or outside, in the waistline direction, of the crotch-side mark portion. a head-side mark portion residing on a side of the main-body third end of a center in the cross direction of the main body portion; and a crotch-side mark portion residing on a side of the main-body fourth end of the center in the cross direction of the main body, characterized in that the head-side mark portion is positioned inside or outside, in the waistline direction, of the crotch-side mark portion.