The Happy Doctor (ごきげんセンちゃんの巻 The Happy Doctor Gokigen Sen-chan no Maki) is the fourth volume of the Dr. Slump manga series written by Akira Toriyama. It was released on April 10, 1981 in Japan and in November 8, 2005 for the English version. This volume most notably deals with the battle against Dodongadon, Senbei and Midori's space date and the year 1980 ending.