Multiple piezoelectric elements 35 are arranged in a row along the top of liquid level in the reaction vessel 11. An ultrasonic reflecting material 38 is installed on the bottom of the portion of the heat insulating bath 12 where heat insulating medium 13 is stored. A lateral ultrasonic wave 9b is generated on the lower side is generated by actuation of the piezoelectric element 35. Wave 9b is reflected by the ultrasonic reflecting material 38. As a lower ultrasonic wave 8 advances along the wall surface of the reaction vessel, it collides with the specimen liquid level, thereby causing a portion of the liquid level closer to the piezoelectric element 35 to be raised. When the lateral ultrasonic wave 9a is applied to this portion, it reaches the inclined portion of the raised liquid level of the specimen. Swirling flow by agitation 36 is produced by the acoustic radiation pressure of the ultrasonic wave. The specimen and reagent are mixed and agitated by this swirling flow.