1. A fuel consumption notification apparatus for a vehicle having an air-conditioning apparatus, the fuel consumption notification apparatus comprising: an acquisition section that acquires an actual fuel consumption rate and a tentative fuel consumption rate from the air-conditioning apparatus, repeatedly during each of a plurality of record periods, the actual fuel consumption rate being a fuel consumption amount per unit time required to generate an electric power that the air-conditioning apparatus consumes under a present preset temperature, the tentative fuel consumption rate being a fuel consumption amount per unit time required to generate an electric power that the air-conditioning apparatus consumes under a post-offset preset temperature, the post-offset preset temperature being obtained by changing the present preset temperature by a predetermined offset temperature, the record period being from when a predetermined record start condition is fulfilled to when a predetermined record end condition is fulfilled; a record section that records in a travel history database each of a plurality of data sets, the each of the plurality of data sets containing an actual fuel consumption accumulation amount and a tentative fuel consumption accumulation amount in the each of the plurality of record periods, the record section collecting the plurality of data sets over the plurality of record periods in the travel history database, the actual fuel consumption accumulation amount being a total fuel consumption amount that is consumed by the air-conditioning apparatus in the each of the plurality of record periods, the actual fuel consumption accumulation amount being calculated based on the actual fuel consumption rate repeatedly acquired by the acquisition section in the each of the plurality of record periods, the tentative fuel consumption accumulation amount being a total fuel consumption amount that is estimated to be consumed by the air-conditioning apparatus in the each of the plurality of record periods under a post-offset preset temperature that is obtained by changing the present preset temperature by the predetermined offset temperature, the tentative fuel consumption accumulation amount being calculated based on the tentative fuel consumption rate repeatedly acquired by the acquisition section in the each of the plurality of record periods; and a notification section that reads the plurality of data sets from the travel history database, and notifies one of (i) the predetermined offset temperature, an actual fuel consumption grand total value, and a tentative fuel consumption grand total value and (ii) the predetermined offset temperature and a difference between the actual fuel consumption grand total value and the tentative fuel consumption grand total value, the actual fuel consumption grand total value being identical or equivalent to a total of the actual fuel consumption accumulation amounts contained in the plurality of data sets, which are read from the travel history database and which are over the plurality of record periods, the tentative fuel consumption grand total value being identical or equivalent to a total of the tentative fuel consumption accumulation amounts contained in the plurality of data sets, which are read from the travel history database and which are over the plurality of record periods.