Making emotional expressions on social media has recently become an ordinary part of life, but sometimes people might send messages with the wrong expression to other people through these media based on unconscious emotions such as anger. However, it is often difficult to recognize these unconscious emotions, and easy to send inappropriate expressions to other people without proper consideration. This could cause an unpleasant experience. To avoid these situations, it is expected that some observable mechanism could detect and communicate the unconscious emotions to the user before they send the message. These days, there are approaches that can detect unconscious emotions using physiological sensors such as EEGs and heartbeat sensors. These approaches provide the procedure to make unconscious emotions observable and communicated to the user in real-time. We apply this technology for detecting the mismatch between the unconscious emotion and expression before sending the message. Based on this idea, we design and implement the mechanism for detecting the mismatch and feed it back to the user of social media. We carry out an experiment using the proposed system. The preliminary result shows that the system tends to be effective for the purpose.