To provide a cutter for forming a flat finished surface (a surface used as a form surface) on a soil cement wall with good work efficiency and with good accuracy.

The cutter 100 for finishing the wall surfaces of the soil cement walls W1, W2 flat includes: a support 20 conveyed and installed substantially vertically on an excavated part excavated along the soil cement walls W1, W2; a movable bed 40 assembled to move up and down along the support 20 and moved up and down by an elevating device 30; a rotary drum 60 rotatably assembled to the movable bed 40 in the substantially horizontal state and driven to rotate by a rotary driving device 50; and a cutting blade 70 integrally provided on the rotary drum 60.