Emotion suppression is a form of conscious inhibition of emotional expressive behavior when a person's emotions are aroused. In human-to-human interaction, problems occur when speakers suppress their emotions; their internal affective states cannot be expressed to the interlocutor. We propose a new recognition technique of emotional suppression that humans may not be able to perceive. In this study, to detect the suppression of negative emotions, we used functional near-infrared spectroscopy and measured cerebral blood flow while participants watched neutral and disgust emotions and then talked about them. For the time-series data of cerebral blood flow, we performed a statistical test to confirm whether there is a significant difference in the mean values and the changes in the cerebral blood flow between each emotion and applied classification models to automatically detect suppressed emotions. Our models correctly detected them with around 60% accuracy.