PURPOSE: To realize a rapid and secure execution by spraying a jelly form concrete made by mixing an admixture and specifying the slump value by using a trowel device.

CONSTITUTION: A boom 8 to rise and fall freely, an arm 10 to rotate freely, a main body 11 of a covering work device, and a concrete hose 13 are provided on a working vehicle 1. While a trowel 12 is provided on the main body 11, an angle variable mechanism of the trowel 12, and a bilateral control system to perceive the squeezing force at the tip of the trowel 12 with an operational lever are arranged. Then, an admixture such as a high polymer binding promoter is mixed to a concrete material, and a jelly form concrete with the slump value 7-15 is made up. The concrete is spray-painted from the nozzle of the trowel 12 to a base rock of a tunnel or the like. Consequently, a good viscosity and an optimum fluidity are secured, a covering work can be carried out securely to the uneven part of the wall surface, and a necessary adhesive force can be obtained at the same time with the spray-painting.