Provided is an antenna-device substrate which is capable of flexibly adjusting multiple resonance frequencies, and also provided is an antenna device. The antenna-device substrate is provided with a substrate main body (2), a ground plane (GND) on the surface of the substrate main body (2), first to third elements (1 to 5), and a short part (6) connecting the first element (3) and the second element (4). The first element is provided with a feed point (FP) at the base end and extends comprising a first connector (C1) of a first passive element (P1). The second element is connected to the ground plane and is provided with a first antenna element (AT1) at the tip end, and extends comprising a second connector (C2) of a second passive element (P2) and comprising a fourth passive element (P4). The third element extends comprising a third connector (C3) of a third passive element (P3). The first element extends with a gap provided between the first element and each of the second element, the third element, and the ground plane such that a floating capacitance can be generated therebetween.