The vessel speed measurement device (1) includes a transducer (20) that transmits ultrasonic waves into water and receives reflected waves of ultrasonic waves, and a signal processing circuit (110) that calculates the speed through water of the vessel on which the transducer (20) is installed, based on the reception signal output from the transducer (20). A target depth at which the speed through water in the vertical direction is substantially zero is identified based on the reception signal. The speed through water in the horizontal direction is acquired with respect to the target depth as the speed through water.