The purpose of this study was to examine effects of well-being cognition technique using mobile app on midlife crisis and subjective well-being among midlife adults. Participants of this study were adults aged 39～60 years. Participants were randomly divided into an experimental group using Well-Being Cognition technique with a smartphone APP application (n = 26) and a control group (n = 26). Experimental treatment was performed three weeks consecutively. Those in the experimental group were required to use Well-Being Cognition smartphone APP every day during the experiment. Before program commencement, participants completed the following scales before and after intervention: Mid-Life Crisis Scale (MLCS), Acceptance and Action Questionnaire (AAQ-16), Negative Affect, Positive Affect, Satisfaction With Life Scale (SWLS), and Life Satisfaction Expectancy Scale (LSES). Repeated Measure analysis of variance was conducted for pre-post values of the two groups to verify interactions between group and time. Results of this study are as follows. First, pre-post differences of Mid-Life Crisis Scale (MLCS) and Negative Affect were significantly decreased compared to those of the control group. Pre-post differences of Acceptance and Action Questionnaire, Positive Affect, Satisfaction With Life Scale (SWLS) and satisfaction Expectancy Scale (LSES) in the experimental group were significantly increased compared to those in the comparative control group. However, the pre-post difference of Positive Affect was not significantly different between the two groups. Finally, meaning of research results and future research direction were discussed.