This May 5 photo shows the visitors at the entrance of Lotte World theme park, which is directly accessible through the underground passage connected to Jamsil Station. (Yonhap)

The busiest subway station in the Seoul Metro system in terms of daily users was Jamsil Station on Line Nos. 2 and 8, the main operator of the metro system for the nation's capital and parts of the surrounding cities said Thursday.

According to the Seoul Metro, 155,229 people used the Jamsil Station between January and April of this year. The state-run company surveyed the ridership for each station, based on the number of people who either entered or exited the system at the said station.

Jamsil Station is located in the affluent district of Songpa-gu. Its proximity to the Lotte World Tower, the Lotte World Theme Park, along with several apartment complexes and school that attributes to the station always bustling with people.

Gangnam Station, on Line No. 2 and Shinbundang Line, had the next highest ridership with 151,607 users per day. Located in Gangnam-gu, it is adjacent to one of the most prominent commercial and business districts south of the Han River.

Gangnam had been the busiest station in last year's survey taken in the same period, with Jamsil coming second. But this year's report showed that the two had switched places.

No. 3 on the list was Hongik Univ. Station with 147,356 users, on Line No. 2, Gyeongui-Jungang Line, and Airport Railway Express. It is close to one of the largest party districts in the city, and the fact that it hosts a Airport Railway means it is always filled with visitors from outside South Korea.

Guro Digital Complex Station (106,564), Seoul Station (105,265), Sillim Station (103,582), Samseong Station (101,475) all surpassed the 100,000-mark in terms of daily users.

In contrast, Dunchon Oryun Station on Line No. 9 had the fewest number of daily users with just 1,465. This is largely attributed to the surrounding areas having very few residential buildings, despite several schools being located near it.

In total, 8.8 million people a day used a subway between January and April.

The number of people who rode the subway for free increased to 91.6 million, from 85.7 million in the same period last year. This is largely due to the increase in the senior population the country went through in recent years, with 19 percent of the population being 65 or above.

In South Korea, any permanent resident aged at least 65 -- including those with foreign nationality -- can use the subway for free.