To make it possible to measure accurately an excavated earth removal volume continuously by using a part of an earth removal pipe as a measuring pipe and measuring the weight of the measuring pipe which is full of removed earth and the flow rate of removed earth and measuring the weight for an unit volume and the removed earth volume for an unit time.

One end of an earth removing pipe 2 which discharges the mud in a propulsive area is opened, thereby constituting partially a measuring pipe 3. A compressed air is supplied to the discharge end of the measuring pipe 3, more specifically, to the inside of a rubber ring provided on the inner peripheral surface of a release end where a discharge control valve 5 is provided so as to expand and shrink as well, thereby controlling the discharge rate in order to fill up earth removal inside the measuring pipe without any clearance. The measuring pipe 3 is arranged to be turnable by way of a swivel joint and designed to measure the partial weight in the measuring pipe 3 with a gravimeter 6, such as a load cell without being affected by the weight of the earth removing pipe 2 and measures the flow rate of earth removal with an ultrasonic current meter 7. The known weight of the measuring pipe 3 is deducted from the measured weight, thereby computing the weight for the unit volume of earth removal and the earth removal volume for the unit time.