Massugu ni Ikou.

Mametarou is a crossbreed male dog kept by Wakatsuki family. He loves his owner Iku (Ikuko Wakatsuki), and considers her boyfriend, Junichi Akiyoshi, as his rival. The manga depicts different incidents happening with Mametarou, Iku and Akiyoshi, their friends Nao and Takeshi, Mametarou’s sweetheart Hanako, as well as other dogs in the neighborhood.
(Source: Japanese Wikipedia)