An object of the present invention is to provide an optical recording/reproducing apparatus capable of improving medium usability through a laser power adjusting process while keeping compatibility with a read only type medium. The optical recording/reproducing apparatus adjusts laser power using a PCA till the PCA is used up. After the PCA is used up, an additional area is reserved at the outermost circumference position, thereafter when the additional area is used up, a new additional area is reserved at an inner circumference side of the used up additional area to adjust laser power. The additional area is reserved at an outer circumference than a lead-out area, and therefore format compatibility with a read only type optical disc can be maintained. The additional area is reserved only when the PCA is used up, thus capacity compatibility with a read only type optical disc can be maintained while laser power is adjusted with only the PCA.