A foreign object detecting device comprising: a coil array that includes coils; short-circuit switches, each of which is connected in parallel with the corresponding coil and each of which is configured to establish or to break an electrical connection between both ends of the coil; selection switches, each of which is configured to establish or to break an electrical connection between the corresponding coil and an oscillator circuit; a detecting circuit configured to detect an amount of change, from a predetermined reference value, in a physical value that changes in accordance with a change in impedance of each of the coils; and a control circuit configured to open and to close each of the short-circuit switches and each of the selection switches, wherein the control circuit is further configured to establish an electrical connection between a first coil included in the coils and the oscillator circuit by closing a first selection switch included in the selection switches and to open a first short-circuit switch included in the short-circuit switches connected in parallel with the first coil, wherein the control circuit is further configured to break an electrical connection between a second coil included in the coils and the oscillator circuit by opening a second selection switch included in the selection switches and to close a second short-circuit switch included in the short-circuit switches connected in parallel with the second coil, and wherein the detecting circuit is configured to detect the amount of change, from the predetermined reference value, in the physical value that changes in accordance with the change in the impedance of the first coil, which is electrically connected to the oscillator circuit and to determine whether there is a foreign object based on the amount of change, characterized in that each of the selection switches is a semiconductor switch, and the control circuit is configured to close the second short-circuit switch so as to increase a current to flow through the first coil. a coil array that includes coils; short-circuit switches, each of which is connected in parallel with the corresponding coil and each of which is configured to establish or to break an electrical connection between both ends of the coil; selection switches, each of which is configured to establish or to break an electrical connection between the corresponding coil and an oscillator circuit; a detecting circuit configured to detect an amount of change, from a predetermined reference value, in a physical value that changes in accordance with a change in impedance of each of the coils; and a control circuit configured to open and to close each of the short-circuit switches and each of the selection switches, wherein the control circuit is further configured to establish an electrical connection between a first coil included in the coils and the oscillator circuit by closing a first selection switch included in the selection switches and to open a first short-circuit switch included in the short-circuit switches connected in parallel with the first coil, wherein the control circuit is further configured to break an electrical connection between a second coil included in the coils and the oscillator circuit by opening a second selection switch included in the selection switches and to close a second short-circuit switch included in the short-circuit switches connected in parallel with the second coil, and wherein the detecting circuit is configured to detect the amount of change, from the predetermined reference value, in the physical value that changes in accordance with the change in the impedance of the first coil, which is electrically connected to the oscillator circuit and to determine whether there is a foreign object based on the amount of change, characterized in that each of the selection switches is a semiconductor switch, and the control circuit is configured to close the second short-circuit switch so as to increase a current to flow through the first coil.