We propose that obsessions are categorized into two subtypes, i.e. autogenous obsessions and reactive obsessions, which are different in terms of identifiability of their evoking stimuli, subjective experiences, contents, and subsequent cognitive processes. Autogenous obsessions tend to come abruptly into consciousness without identifiable evoking stimuli, which are perceived as ego-dystonic and aversive enough to be repelled, and include sexual, aggressive, and immoral thoughts or impulses. On the other hand, reactive obsessions are evoked by identifiable external stimuli, which are perceived as relatively realistic and rational enough to do something toward the stimuli, and include thoughts about contamination, mistake, accident, asymmetry, loss, etc. Through three empirical studies, we confirmed the differences between the two types of obsessional intrusion in their frequency, subjective experiences, subsequent appraisal and control strategy. In particular, autogenous obsessions led to high appraisal on 'control over thought' and 'importance of thought' and frequent use of 'avoidant control strategies', while reactive obsessions linked with high appraisal on 'responsibility' and frequent use of 'confrontational control strategies'. These findings are expected to provide a basis for classifying and explaining the heterogeneous phenomena of obsessive-compulsive disorder.