Prediction performance evaluation is an essential step in machine learning model development. Model performance is generally assessed based on the number of correct and incorrect predictions it makes. However, this evaluation metric has a limitation in that it treats all cases equally, regardless of their varying levels of prediction difficulty. In this paper, we propose novel prediction performance metrics considering the prediction difficulty. The novel performance metrics reward models for correct predictions on difficult cases and penalize them for incorrect predictions on easy cases. The prediction difficulty of individual cases is measured using three case difficulty calculation metrics developed by neural networks. We conducted experiments using a variety of datasets and seven machine learning models to compare prediction performance with and without considering the difficulty of individual cases. The experimental results demonstrate that our novel prediction performance metrics enhance the understanding of model performance from various aspects and provide a more detailed explanation of model performance than conventional performance metrics.