PURPOSE: To provide a pit excavating device which can well work with a casing tube having a large bore and can exert traveling of good mobility even on a narrow road, etc., by structuring a swing pressure fit mechanism so that its width can be reduced.

CONSTITUTION: Booms 18a, 18b are connected with a mobile dolly 1 in such a way that they can tilt, and an excavating machine 21 is supported suspendedly through wires 23, 23. A swing pressure fit mechanism 2 is installed in the front part of the dolly 1, and a casing tube T is clamped, swung, and fitted in by pressure. Thus a pit excavating device is configured, wherein the swing pressure fit mechanism 2 is formed so that its width can be reduced. At the time of pressure fitting with swings, the mechanism 2 is widened to a size to enable clamping of the casing tube T, and is shrunk to a width which suits traveling when out of service.