As a result of amendments to the Health Promotion Act, smoking was prohibited in schools, hospitals, and government buildings from July 2019, and in principle, smoking was prohibited in offices, factories, and restaurants from April 2020. Previous studies have pointed out the health hazards of smoking and the loss of productivity through smoking breaks, absence from work and presenteeism, but few papers have shown a causal relationship. In this study, we conducted a smoking cessation support program for employees of a manufacturing company and evaluated the effects on health, productivity, and the workplace. Of the 73 participants, 44 were eligible for smoking cessation support (treatment group), of whom 33 successfully quit smoking, meaning a 75% success rate. We find that participation in the smoking cessation program reduced smoking break time by 27 minutes per day, and for those who actually quit smoking, by approximately 50 minutes per day. Smoking cessation was also shown to improve presenteeism by 0.5 standard deviations, reduce stress by 0.9 standard deviations, and decrease the number of sick days and days left early due to health problems in the past month by 0.5 and 0.4 days, respectively, although the differences for absenteeism were significant only at the 10% level. The results imply that smoking cessation boosts productivity even in the short term through the elimination of smoking breaks, improved presenteeism, and reduced absenteeism.