A 47-year-old man who suffered from fever and dry cough visited a local clinic. His symptoms temporarily improved with oral administration of ciprofloxacin, however, he was admitted to our hospital because of exacerbation. IgM antibody for Mycoplasma pneumoniae was positive and IgM antibody titer for Chlamydophila pneumoniae showed a high value of 7.12 index. Thus, coinfection was diagnosed. The findings of chest X-ray and computed tomography were compatible with atypical pneumonia. Clarithromycin improved his condition, and 10 weeks later, antibody values for Mycoplasma pneumoniae by the particle agglutination test decreased from 10,240 times to 640 times and those by the complement-fixation test also decreased from 1024 times to 256 times. The IgM antibody for Chlamydophila pnetumoniae decreased to 0.13. This is the first case developing coinfection with Mycoplasma pneumoniae and Chlamydophila pneumoniae in a middle-aged patient to date.