Actually gold price never increase, but fiat always inflation.
Exactly.
The value of an investment is not how many US dollars, Euros, Yen etc. that investment is worth.
The value of an investment is how much bread and milk you can buy with it.
Gold's value is the quantity of goods or services you can buy with a certain quantity of gold, for example an ounce.
That is gold's buying power.
Gold's value, it's buying power remains the same.
As fiat currencies depreciate, their buying power decreases, therefore the gold's price, which is the exchange rate between gold and fiat currencies, increases.