A drive assistant (700) executes a drive assist function that is a function of a drive assist system. A first electronic control apparatus (401) has a first sensor (501). A second electronic control apparatus (402) has a second sensor (502). The first electronic control apparatus (401) is connected to the drive assistant (700) via a main network (10). The second electronic control apparatus (402) is connected to the first electronic control apparatus (401) via a sub-network (20) having no connection to the drive assistant (700). The first electronic control apparatus (401) outputs, to the main network (10), control assist information generated on the basis of first sensing information acquired by the first sensor (501) and second sensing information acquired by the second sensor (502).