The reason Japan still uses a voltage of 100V (specifically 100V) is quite an interesting mix of historical background and practical reasons.

Let's summarize the answer to the question, "Why does Japan use 100V when most of the world uses 220V?"

Reasons Japan Uses 100V

Japan first introduced electricity in 1878. At that time, Tokyo had a German-style 50Hz system, and Osaka had an American-style 60Hz system.

In other words, the country was divided into two frequencies, and the voltage began to follow the 100V standard based on the generators imported from the United States.
This is the root of Japan's voltage system that continues to this day.

For reference, Japan is still the only country in the world that uses two frequencies: 50Hz in Tokyo (east) and 60Hz in Osaka (west).

100V became the standard by the time home appliances were popularized

After the 1920s and 30s, as electric appliances rapidly spread in Japan, most products were made based on the 100V standard.
Since then, air conditioners, rice cookers, refrigerators, TVs, and everything else has been adjusted to this standard, so there was no reason to change it.

Lower voltage means lower risk of electric shock

100V is the lowest voltage among major countries in the world.
This means that the shock to the human body during an electric shock is relatively less.

Japan is a country prone to disasters such as earthquakes and fires, and a system designed with electrical safety in mind fits well with this.
Additionally, the housing structure and wiring methods are designed very densely and delicately to match the Japanese 100V voltage.

There were plans to increase the voltage, but...

In fact, in the mid-20th century, the Japanese government once planned to increase the voltage to over 200V.
But the reality is...

• The enormous cost of replacing all the national wiring, transformers, and appliances

• Too many households and industries had already become accustomed to 100V

Ultimately, this voltage increase plan was not implemented and fell through.
Now, only some high-power devices (like air conditioners and dryers) use separate 200V outlets as a compromise.

"Japan did not change because it could, but because it has come too far to turn back."
The decision to prioritize safety in daily life and system stability over efficiency in power usage continues to this day.

And one of the secrets behind the unique 'unbreakable Japanese appliances' is largely due to this stable 100V system.