An in-vehicle apparatus installed in a first vehicle. The in-vehicle apparatus includes a first distance sensor measuring a distance to an object based on time to receive a reflection wave of an electro-magnetic transmission wave from the object after a transmission of the electro-magnetic transmission wave, with the first distance sensor being an electro-magnetic wave sensor. The in-vehicle apparatus also includes an inclination angle sensor that senses a first vehicle inclination angle representative of an inclination angle of the first vehicle that includes the first distance sensor, a radio communicator that receives a second vehicle inclination angle transmitted from a second vehicle that leads the first vehicle, an angle difference calculator that calculates an angle difference between the first vehicle inclination angle and the second vehicle inclination angle, and a processor that performs a preset operation based on the distance measured by the first distance sensor.