There is provided a pulse wave detector enabling pulse wave detection with reduced power consumption, and prolonged usage time. Ultrasonic waves having a frequency of 10 MHz are transmitted from a transmitter towards an artery, and reflected waves that have undergone frequency modulation as a result of the Doppler effect of the artery are received by a receiver, pulse waves are extracted by FM detection, and a pulse rate is counted and displayed. Transmission of ultrasonic waves by the transmitter and reception of reflected waves by the receiver are carried intermittently at a frequency of 64 Hz to reduce the power consumption, to enable installation even in a small portable device with low battery capacity such as a watch, and to enable prolonged usage time. The transmitter and receiver have a rectangular shape and are arranged so that a long axis crosses the artery, which means that measurement of pulse waves can be continued without the need to correct positioning even if the artery or a sensor position shifts laterally.