The present invention is an animal litter box 1 configured to have a front/rear direction, a left/right direction, and a height direction, and provided with the following: a urine passage section 21 to which a plurality of holes 210 through which urine passes are provided, and in which an excrement treatment material is installed； an absorber installation section 31 which is provided lower than the urine passage section 21 and in which an absorber is installed； an opening 41 which is provided higher than the urine passage section 21, and through which an animal enters and exits； and a side wall 4a provided to both left and right sides of the opening 41. A maximum height H1 of the side wall 4a in a front region 11 further frontward than a middle position C in the front/rear direction is smaller than a minimum height h2 of the side wall 4a in a rear region 12 further rearward than the middle position C, and a maximum opening width W1 of the opening 41 in the front region 11 is greater than a maximum opening width W2 of the opening 41 in the rear region 12.
