To suppress a possibility of electromagnetic waves becoming difficult to pass through a heat-generating band.SOLUTION: A heater sheet 6 is attached to an onboard sensor cover located forward in a mill-wave transmission direction of a mill-wave radar. The heater sheet 6 includes a sheet substrate 7 attached to the onboard sensor cover and a heat-generating band 8 provided along the sheet substrate 7. The heat-generating band 8 is formed in a shape of a mesh where a large number of filamentous first and second conductors 12, 13 are crossed. The first and second conductors 12, 13 are formed so that these are tilted with respect to a horizontal direction. With this heater sheet 6, the first and second conductors 12, 13 in the heat-generating band 8 never extend in the horizontal direction, so that there is not generated such a situation in which, the electromagnetic wave transmitted from the mill-wave radar so as to expand in the horizontal direction becomes difficult to pass through the heat-generating band 8 by interfering with the conductors extending in the horizontal direction in the heat-generating band 8.SELECTED DRAWING: Figure 3