To provide a radio sensor device which can prevent electromagnetic noise from entering an antenna, despite that the overall configuration is made compact.

The antenna 6 comprises a support substrate 60 and antenna conductors 61 to 64. The support substrate 60 is made of an electrical insulating material. The antenna conductors 61 to 64 are helical and move in a direction parallel to the plane of the support substrate 60 helically winding, with the thickness of the support substrate 60 as two sides of an opening. The area of the opening is substantially determined by the product XY of the effective length X of a first conductor piece 61 and a second conductor piece 62 and the effective length Y of a third conductor piece 63 and a fourth conductor piece 64.

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