PURPOSE: To built an underground wall having no portion deficient in strength, but high reliability by making the lift speed of a lift frame constant and setting the rotational speed of a excavating start in inverse proportion to a braking current of a winch motor.

CONSTITUTION: An underground wall executing machine controls the lift speed of a lift frame 12 holding a plurality of excavating shafts 171-175 to be preset constant speed. Also, the rotational speed of the excavation shafts 171-175 is controlled to be changed in inverse proportion to the braking current of winch motor 18L, 18R for driving the lift frame 12. Thus, while the lift frame 12 is lowered with the constant speed in the penetration of the excavating shafts 171-175, the rotational frequency of the excavating shaft 171-175 is increased in the hard portion of soil in the direction of the underground depth to stir sufficiently the soil even in the hard portion of the soil, so that the soil and a coagulating agent can be unformly mixed with each other even in the hard portion of soil.