The highest-selling singles in Japan are ranked in the Oricon Singles Chart, which is published by Oricon Style magazine. The data are compiled by Oricon based on each singles' physical sales. This list includes the singles that reached the number one place on that chart in 1978.
| Issue date | Song | Artist(s) | Ref. |
|---|---|---|---|
| January 2 | "UFO" | Pink Lady | [1] |
| January 9 | |||
| January 16 | |||
| January 23 | |||
| January 30 | |||
| February 6 | |||
| February 13 | |||
| February 20 | |||
| February 27 | "Canada Kara no Tegami" | Masaaki Hirao & Yōko Hatanaka | |
| March 6 | |||
| March 13 | "Hohoemi Gaeshi" | Candies | |
| March 20 | |||
| March 27 | |||
| April 3 | "Southpaw" | Pink Lady | |
| April 10 | |||
| April 17 | |||
| April 24 | |||
| May 1 | |||
| May 8 | |||
| May 15 | |||
| May 22 | |||
| May 29 | |||
| June 5 | "Darling" | Kenji Sawada | |
| June 12 | "Jikan yo Tomare" | Eikichi Yazawa | |
| June 19 | |||
| June 26 | |||
| July 3 | "Mr. Summertime" | Circus | |
| July 10 | "Monster" | Pink Lady | |
| July 17 | |||
| July 24 | |||
| July 31 | |||
| August 7 | |||
| August 14 | |||
| August 21 | |||
| August 28 | |||
| September 4 | "Hikigane" | Masanori Sera & Twist | |
| September 11 | "Kimi no Hitomi wa 10,000 Volt" | Takao Horiuchi | |
| September 18 | |||
| September 25 | |||
| October 2 | "Tomei Ningen" | Pink Lady | |
| October 9 | "Kimi no Hitomi wa 10,000 Volt" | Takao Horiuchi | |
| October 16 | "Tomei Ningen" | Pink Lady | |
| October 23 | |||
| October 30 | |||
| November 6 | "Kisetsu no Naka de" | Chiharu Matsuyama | |
| November 13 | |||
| November 20 | |||
| November 27 | |||
| December 4 | |||
| December 11 | |||
| December 18 | "Chameleon Army" | Pink Lady | |
| December 25 |