The in-vehicle control device includes first and second control units that perform first and second controls, respectively; first and second sensors for measuring the same physical quantity, and a transmission channel for communicating information between the first control unit and the second control unit. Outputs from the first and the second sensors are taken in and used for the first and the second controls by the first and the second control units, respectively. The first and the second control units repeatedly perform diagnoses of the first and the second sensors, respectively, and receive each results of measurements of the physical quantity measured based on the outputs of the first and the second sensors, respectively, through the transmission channel.