A 47-year-old man was found to have abnormal findings on chest radiography. Chest computed tomography (CT) and magnetic resonance imaging (MRI) showed that he had a pulmonary arteriovenous malformation. He had experienced epistaxis when he was a junior high school student, and since then, the symptom had frequently recurred. Further, he had telangiectasia on the lips. Thus, he was given a diagnosis of hereditary hemorrhagic telangiectasia (HHT). Endoscopy revealed gastric telangiectasia, and in addition, his colon had many juvenile polyps. When he was 49 years of age, he underwent genetic analysis for HHT. A diagnosis of juvenile polyposis-HHT combined syndrome (JP-HHT) was made since a heterozygous germline 4-base deletion in exon 9 of SMAD4 was detected. To the best of our knowledge, this is the first case of JP-HHT associated with SMAD4 mutation in Japan.