This paper describes a study of new blood pressure estimation based on heartbeat signal that is captured by bi-directional microphones. In order to detect heartbeat signal by using a microphone, one side of the microphone is sealed to enhance the sensitivity of the heartbeat signal. Preliminary experiments are carried out to detect heartbeat from finger and neck artery. According to the heartbeat phase difference between finger and neck artery, we found relation between heartbeat phase and blood pressure are highly correlated. Validity of proposed blood pressure measurement method is confirmed by actual measurement.