An electronic control apparatus (40; 60) comprising: a main integrated circuit (41; 61), comprising a power source terminal (Td) coupled to receive an externally supplied power source voltage, a voltage step-up circuit operating from said power source voltage supplied to said power source terminal to produce a stepped-up voltage that is higher than said power source voltage, a stepped-up voltage output terminal (To) coupled to receive said stepped-up voltage, and first drive circuit means (11, 12) for selectively applying said stepped-up voltage to a gate electrode of a first MOS FET (1, 2) that is connected in a current flow path of a first electrical load, to effect on and off switching of said first MOS FET; at least one auxiliary integrated circuit (42, 43; 62, 63), comprising a stepped-up voltage input terminal (Ti) coupled to receive said stepped-up voltage from said stepped-up voltage output terminal of said main integrated circuit, and second drive circuit means (13 to 15) for selectively applying said stepped-up voltage to a gate electrode of a second MOS FET (3 to 5) that is connected in a current flow path of a second electrical load, to effect on and off switching of said second MOS FET; and noise reduction means coupled to said power source input terminal of said main integrated circuit, wherein at least one circuit element that is a constituent element of said voltage step-up circuit and whose value determines an operating period of said voltage step-up circuit is connected to said main integrated circuit as an external component, and wherein the electric power is supplied from the power source voltage to the MOS FETs, while the voltage step-up circuit is supplied with the power from the power source voltage through the noise reduction means. a main integrated circuit (41; 61), comprising a power source terminal (Td) coupled to receive an externally supplied power source voltage, a voltage step-up circuit operating from said power source voltage supplied to said power source terminal to produce a stepped-up voltage that is higher than said power source voltage, a stepped-up voltage output terminal (To) coupled to receive said stepped-up voltage, and first drive circuit means (11, 12) for selectively applying said stepped-up voltage to a gate electrode of a first MOS FET (1, 2) that is connected in a current flow path of a first electrical load, to effect on and off switching of said first MOS FET; a power source terminal (Td) coupled to receive an externally supplied power source voltage, a voltage step-up circuit operating from said power source voltage supplied to said power source terminal to produce a stepped-up voltage that is higher than said power source voltage, a stepped-up voltage output terminal (To) coupled to receive said stepped-up voltage, and first drive circuit means (11, 12) for selectively applying said stepped-up voltage to a gate electrode of a first MOS FET (1, 2) that is connected in a current flow path of a first electrical load, to effect on and off switching of said first MOS FET; at least one auxiliary integrated circuit (42, 43; 62, 63), comprising a stepped-up voltage input terminal (Ti) coupled to receive said stepped-up voltage from said stepped-up voltage output terminal of said main integrated circuit, and second drive circuit means (13 to 15) for selectively applying said stepped-up voltage to a gate electrode of a second MOS FET (3 to 5) that is connected in a current flow path of a second electrical load, to effect on and off switching of said second MOS FET; and a stepped-up voltage input terminal (Ti) coupled to receive said stepped-up voltage from said stepped-up voltage output terminal of said main integrated circuit, and second drive circuit means (13 to 15) for selectively applying said stepped-up voltage to a gate electrode of a second MOS FET (3 to 5) that is connected in a current flow path of a second electrical load, to effect on and off switching of said second MOS FET; and noise reduction means coupled to said power source input terminal of said main integrated circuit, wherein at least one circuit element that is a constituent element of said voltage step-up circuit and whose value determines an operating period of said voltage step-up circuit is connected to said main integrated circuit as an external component, and wherein the electric power is supplied from the power source voltage to the MOS FETs, while the voltage step-up circuit is supplied with the power from the power source voltage through the noise reduction means.