Object detection is a fundamental task in computer vision that has received significant attention in recent years. Despite advances in training object detection models, evaluating their performance in real-world applications remains challenging due to the substantial costs associated with image annotation. To address this issue, we propose Prediction Consistency and Reliability (PCR) as an automated model evaluation (AutoEval) method for object detection. Our method is motivated by the observation that most existing object detection models generate many candidate predictions, which are subsequently filtered through non-maximum suppression (NMS). Specifically, we analyze 1) the consistency between the final and redundant predictions and 2) the reliability of these predictions determined by their confidence scores, and propose PCR by examining their relationships with object detection performance. Furthermore, to facilitate a more realistic assessment of AutoEval methods for object detection, we construct meta-datasets incorporating various corruptions. Experimental results demonstrate the superior performance of PCR compared to the existing AutoEval methods.