Abstract: An apparatus for measuring the depth of water and the water temperature at any point of an open channel by measuring an ultrasonic propagation time transmitted between a plural number of ultrasonic transducers and by a calculation using an ultrasonic velocity, wherein a slider 11 is attached to a support 13 capable of moving up and down, which is placed in water. A first ultrasonic transducer 18 is fixed to the bottom of the support 13 and a second ultrasonic transducer 19 is positioned above the first ultrasonic transducer 18. A third ultrasonic transducer 21 is positioned above the second ultrasonic transducer 19 and below the slider 11 and a fourth ultrasonic transducer 22 is fixed to the slider 11. Each transducer faces with each other. The apparatus further comprises a fifth transducer 23 and a sixth transducer 24 for measuring the flow velocity, both of which transmit and receive ultrasonic waves.