An information transmission method in a client device (2002) provided in a mobile object includes: obtaining sensor information that has been obtained by a sensor provided in the mobile object and indicates a surrounding state of the mobile object, and storing the sensor information into a storage (2012) (S2001); determining whether the mobile object is present in an environment in which the mobile object is capable of transmitting the sensor information to a server (2001) (S2002); and transmitting the sensor information to the server (2001) when the mobile object is determined to be present in the environment in which the mobile object is capable of transmitting the sensor information to the server (2001) (YES in S2002) (S2003).