An in-vehicle apparatus includes a processor configured to obtain first transmission data with a first communication address as a destination and second transmission data with a second communication address as a destination from one or more applications, transmit the first transmission data to a relay unit at a first timing among a plurality of timings set at an interval of a predetermined cycle corresponding to a buffer size of the relay unit to which the in-vehicle apparatus is connected, and transmit the second transmission data to the relay unit at a second timing among the plurality of timings, the second timing being different from the first timing.