Karatsu Line
On 1 December 1898, the Karatsu Kogyo Railway had opened a track from Miyoken (now ) to . On 13 June 1899, the track was extended to with this station, at that time named Motoyama, opening on the same day as an intermediate station on the track. On 23 February 1902, the company, now renamed the Karatsu Railway, merged with the Kyushu Railway. On 1 November 1903, the station was renamed Iwaya. When the Kyushu Railway was nationalized on 1 July 1907, Japanese Government Railways (JGR) took over control of the station. On 12 October 1909, the line which served the station was designated the Karatsu Line. With the privatization of Japanese National Railways (JNR), the successor of JGR, on 1 April 1987, control of the station passed to JR Kyushu.