A coil device configured to be used in a wireless power transfer system comprising: a coil portion (T) including at least a coil formed by a conductive wire ; a housing (C) including a plate-shaped base disposed on a side of a first surface (T1) of the coil portion (T) and a cover disposed on a side of a second surface (T 2 ) opposite of the coil portion (T) and accommodating the coil portion (T) in an internal space (S) formed by the base and the cover , whereby the first surface (T1) and the second surface (T2) are parallel to a horizontal plane extending in an X- and Y-direction; and a fixing member fixing the cover to the base , wherein the fixing member has opposite end portions , the fixing member includes a first fixing portion disposed along at least the cover (11, 11B, 11C, 11D, 11E 11) on a first outer periphery (R1) of the housing (C) surrounding the base and the cover , wherein the coil device is configured to be attached to a vehicle (V) such that the cover is on a lower side, and the base is on an upper side adjacent to the vehicle, as seen in a vertical Z-direction of the vehicle, wherein the fixing member includes an intermediate portion disposed along a bottom portion of the cover , the bottom portion facing the second surface T2 of the coil portion, a connecting portion extending along the Z-direction and disposed along a side portion of the cover and a side portion of the base , and both end portions disposed along a plate portion of the base , wherein the first outer periphery (R1) is an outer periphery surrounding the housing (C) by using the Y-direction as an axis for surrounding, the outer periphery passing through a middle portion (M2) of the cover and a middle portion (M1) of the base , the middle portion (M1) of the cover and the middle portion (M2) of the base facing the first surface (T1) and the second surface (T2), and the fixing member is in planar contact with the cover in the intermediate portion and the connecting portion . a coil portion (T) including at least a coil formed by a conductive wire ; a housing (C) including a plate-shaped base disposed on a side of a first surface (T1) of the coil portion (T) and a cover disposed on a side of a second surface (T 2 ) opposite of the coil portion (T) and accommodating the coil portion (T) in an internal space (S) formed by the base and the cover , whereby the first surface (T1) and the second surface (T2) are parallel to a horizontal plane extending in an X- and Y-direction; and a fixing member fixing the cover to the base , wherein the fixing member has opposite end portions , the fixing member includes a first fixing portion disposed along at least the cover (11, 11B, 11C, 11D, 11E 11) on a first outer periphery (R1) of the housing (C) surrounding the base and the cover , wherein the coil device is configured to be attached to a vehicle (V) such that the cover is on a lower side, and the base is on an upper side adjacent to the vehicle, as seen in a vertical Z-direction of the vehicle, wherein the fixing member includes an intermediate portion disposed along a bottom portion of the cover , the bottom portion facing the second surface T2 of the coil portion, a connecting portion extending along the Z-direction and disposed along a side portion of the cover and a side portion of the base , and both end portions disposed along a plate portion of the base , wherein the first outer periphery (R1) is an outer periphery surrounding the housing (C) by using the Y-direction as an axis for surrounding, the outer periphery passing through a middle portion (M2) of the cover and a middle portion (M1) of the base , the middle portion (M1) of the cover and the middle portion (M2) of the base facing the first surface (T1) and the second surface (T2), and the fixing member is in planar contact with the cover in the intermediate portion and the connecting portion . <EOS>