An apparatus and method for easily and accurately measuring a biological signal by using a wristwatch-type measurement module. After a band of the wristwatch-type measurement module is tightened to wear on a users wrist, the band is further tightened to make the wristwatch-type measurement module closely contact the users wrist. An operation mode of the wristwatch-type measurement module closely contacting the users wrist is switched from a normal mode to a measurement mode, and a users biological signal is measured from the users wrist through the wristwatch-type measurement module in the measurement mode. The users biological signal is then displayed through the wristwatch-type measurement module.
