A foreign object detection device for a coil device used for wireless power transfer from a power transmitter, the foreign object detection device comprising: first and second detection coils configured to be disposed on a casing of the coil device, each of the first and second detection coils including two terminals (A, B); a selector configured to select one of one terminal of the first detection coil and one terminal of the second detection coil as a first terminal and select one of the other terminal of the first detection coil and the other terminal of the second detection coil as a second terminal; and a controller (14, 16) configured to perform a first foreign object determination process that causes the selector to select the one terminal of the first detection coil as the first terminal and the other terminal of the second detection coil as the second terminal to determine whether there is an electrically conductive foreign object depending on whether connection between the first terminal and the second terminal is in a short circuit state or an open state, and to perform a second foreign object determination process that causes the selector to select the two terminals of the same detection coil from either the first detection coil and the second detection coil as the first terminal and the second terminal to determine whether there is the foreign object depending on a change in an amount of magnetic flux interlinking with the same detection coil, wherein in the first foreign object determination process the controller (14, 16) is configured to determine that there is the foreign object in a case where the connection between the first terminal and the second terminal is a short circuit state, and wherein in the second foreign object determination process the controller (14, 16) is configured to determine that there is the foreign object in a case where the amount of magnetic flux changes as compared with an amount of magnetic flux when there is not the foreign object. first and second detection coils configured to be disposed on a casing of the coil device, each of the first and second detection coils including two terminals (A, B); a selector configured to select one of one terminal of the first detection coil and one terminal of the second detection coil as a first terminal and select one of the other terminal of the first detection coil and the other terminal of the second detection coil as a second terminal; and a controller (14, 16) configured to perform a first foreign object determination process that causes the selector to select the one terminal of the first detection coil as the first terminal and the other terminal of the second detection coil as the second terminal to determine whether there is an electrically conductive foreign object depending on whether connection between the first terminal and the second terminal is in a short circuit state or an open state, and to perform a second foreign object determination process that causes the selector to select the two terminals of the same detection coil from either the first detection coil and the second detection coil as the first terminal and the second terminal to determine whether there is the foreign object depending on a change in an amount of magnetic flux interlinking with the same detection coil, wherein in the first foreign object determination process the controller (14, 16) is configured to determine that there is the foreign object in a case where the connection between the first terminal and the second terminal is a short circuit state, and wherein in the second foreign object determination process the controller (14, 16) is configured to determine that there is the foreign object in a case where the amount of magnetic flux changes as compared with an amount of magnetic flux when there is not the foreign object.