To provide an ultrasonic Doppler echo device with alarm for detecting the occurrence of a pulmonary thrombus/embolism since there is no detector for such a disease to occur after a surgical operation at present.

An ultrasonic echo sensor installed on the walls of the chest of a patient is altered into form to be turned toward a direction where the pulmonary artery can be observed at all times. Then, the blood velocity of the pulmonary artery in the trunk of the pulmonary artery is continuously measured by this ultrasonic Doppler echo device, the deceleration of the blood velocity caused by the occurrence of the thrombus in the pulmonary artery is sensed, an alarm is sounded and a caution is raised to a medical worker.