Róbert Homolya, who heads state-owned railway company MÁV, said almost 8 million passengers travel along the line each year.
Nine more of the KISS trains will operate on the line by the end of 2022, he added.
Ten of the KISS trains already operate on the Budapest-Vác line that runs to the north of the capital, and four on the Budapest-Cegléd line, in the southeast.
Hungary ordered 40 of the KISS trains from Switzerland's Stadler in 2017. The last will be delivered by the end of next year.