A vehicular display device including display means , control means for performing display control of the display means , a non-volatile memory storing at least an operation program of the control means and image data to be displayed on the display means , and a third connection terminal (C3) connectable to both a first connection terminal (CN1) and a second connection terminal (CN2) having different terminal arrangements, the vehicular display device being housed in an instrument panel of a vehicle, comprising: an external device configured to connect the first connection terminal (CN1) or the second connection terminal (CN2) to the third connection terminal (CN3) to communicate with the control means , a fourth connection terminal (CN4) different from the third connection terminal (CN3); and a latch configured to rewrite a permission state of rewriting to the non-volatile memory via the fourth connection terminal (CN4) and hold the permission state, wherein the control means switches permission/non-permission of rewriting to the non-volatile memory in accordance with the state held by the latch and a type of the connection terminal connected to the third connection terminal (CN3), wherein the control means communicates diagnosis information to the external device via the fourth connection terminal (CN4); and the latch allows the external device to rewrite the permission state of rewriting to the non-volatile memory via the control means . control means for performing display control of the display means , a non-volatile memory storing at least an operation program of the control means and image data to be displayed on the display means , and a third connection terminal (C3) connectable to both a first connection terminal (CN1) and a second connection terminal (CN2) having different terminal arrangements, the vehicular display device being housed in an instrument panel of a vehicle, comprising: an external device configured to connect the first connection terminal (CN1) or the second connection terminal (CN2) to the third connection terminal (CN3) to communicate with the control means , a fourth connection terminal (CN4) different from the third connection terminal (CN3); and a latch configured to rewrite a permission state of rewriting to the non-volatile memory via the fourth connection terminal (CN4) and hold the permission state, wherein an external device configured to connect the first connection terminal (CN1) or the second connection terminal (CN2) to the third connection terminal (CN3) to communicate with the control means , a fourth connection terminal (CN4) different from the third connection terminal (CN3); and a latch configured to rewrite a permission state of rewriting to the non-volatile memory via the fourth connection terminal (CN4) and hold the permission state, wherein the control means switches permission/non-permission of rewriting to the non-volatile memory in accordance with the state held by the latch and a type of the connection terminal connected to the third connection terminal (CN3), wherein the control means communicates diagnosis information to the external device via the fourth connection terminal (CN4); and the latch allows the external device to rewrite the permission state of rewriting to the non-volatile memory via the control means . <EOS>