A weakly supervised object localization apparatus includes: a feature map generator configured to generate a feature map X by performing a first convolution operation on an input image; an erased feature map generator configured to generate an attention map A through the feature map X and generate an erased feature map −X by performing a masking operation on the input image through the attention map A; a final map generator configured to generate a final feature map F and a final erased feature map −F, respectively, by performing a second convolution operation on the feature map X and the erased feature map −X; and a contrastive guidance determiner configured to determine contrastive guidance for a foreground object in the input image based on the final feature map F and the final erased feature map −F.