Abstract Background : Alexithymia is a central concept in psychosomatic disorders, but its treatment has not been established. Therefore, in order to clarify the details of the pathogenesis of alexithymia for further treatment, the present study aimed to evaluate the association between alexithymia pathophysiology, classified by the presence or absence of alexithymia as assessed by the 20-item version of The Toronto Alexithymia Scale (TAS-20), and emotional expressive process functioning as assessed by Japanese version of the Difficulties in Emotion Regulation Scale (J-DERS). Methods : From February 2018 to June 2019, first-time patients aged 16 years or older referred to our department were eligible for inclusion, and patients with mental illness, patients who declined to provide information, and those who consented but failed to complete the form were excluded. The comparison between the median J-DERS total and subscale scores of the TAS-20 high-scoring group (defined as >-52 points) and the TAS-20 low-scoring group (defined as <-51 points) was set as the primary outcome. J-DERS total score and subscales were used as dependent variables, and multiple linear regression analysis was used to analyze the association with the subscales of the TAS-20. Results : Of the 188 total subjects, 106 (56%) were included in the analysis. On the median total J-DERS score, the TAS-20 high scoring group was significantly higher than the low scoring group. Similarly, a significant difference was seen with each J-DERS subscale. Of the three TAS-20 subscales, only difficulty in identifying feelings correlated with the J-DERS total score and subscales. Conclusions : Although alexithymia has been considered to be a disruption in one of steps of the emotional expression process, the results of our study revealed that alexithymia affects the several emotional expression process. Future research may help treat alexithymia by providing psychotherapy that is commensurate with each step of the emotional expression process.