The semiconductor integrated circuit device includes a T-type switch circuit TS[k] that is between an input port A[k] and an input terminal Ain of an analog/digital conversion circuit and that includes first, second, and third PMOS transistors MP1, MP2, and MPc, and first, second, and third NMOS transistors MN1, MN2, and MNc; and a fourth PMOS transistor MPu for pre-charging the input terminal Ain to a power supply voltage VCCA. In detecting the presence or absence of a disconnection from the input port A[k] to a signal input terminal Vint[k], first, the input terminal Ain is pre-charged to the power supply voltage VCCA via the fourth PMOS transistor MPu and also the second NMOS transistor MN2 and the second PMOS transistor MP2 are turned on, and the first NMOS transistor MN1, the first PMOS transistor MP1, the third PMOS transistor MPc, and third the NMOS transistor MNc are turned off.