In recent years, sales of electric dishwashers for household use (called dishwashers) have increased rapidly due to the increasing number of women in the workplace and also to the appeal of these devices in reducing housework. For these reasons, dishwashers have become popular within a short period of time. This study examined the environmental load of dishwashing using one old and one new dishwasher compared with washing by hand, under conditions of constant cleaning efficiency, and examined ways to reduce the environmental load of dishwashing. Cleaning efficiency was evaluated after washing using the BLT-DW method and the ATP method. In addition, the average amounts of power and water consumed for one dishwashing were also measured. As a result, it became clear that the amounts of CO₂ emissions during use greatly exceeded the amounts of CO₂ emissions during manufacturing for both dishwashers, regardless of the age of the dishwasher or the dishwashing program selected. In addition, the CO₂ emissions attributable to power consumption comprised the highest group of such emissions compared with emissions corresponding to the use of detergent and water. A method that included presoaking for 20 min was shown to reduce CO₂ emissions significantly by reducing the amount of detergent used, although the total amount of water used increased. Therefore, we confirmed that presoaking was an effective method for reducing the environmental load when using dishwashers. The CO₂ emissions through dishwashing by hand in cold water were shown to be approximately 25% of those generated using a dishwasher. However, it became clear that the CO₂ emissions for dishwashing by hand exceeded those of a dishwasher if the water was gas-heated by 5°C or more. Therefore, it was confirmed that dishwashing using a dishwasher represented a more environmentally-friendly method in the winter, when water is cold.