The present invention relates to an industrially preferable process for producing an indolopyrrolocarbazole derivative represented by the formula (I): or a pharmaceutically acceptable salt thereof, which is useful as an anti-cancer agent. The above process comprises treating a compound represented by the formula (V): or a pharmaceutically acceptable salt thereof, a solvate thereof or a salt thereof, with a base in an inert solvent, followed by treatment with an acid, and further treating the resulting reaction solution with a base in an inert solvent and subsequently with an acid, and then reacting the resulting compound with an acid addition salt of hydrazine diol in the presence of an acid scavenger, followed by removal of protecting group(s) from the resulting compound.