Key Inclusion Criteria  Japanese participants ≥ 20 years of age upon entry into initial screening Palmoplantar pustulosis diagnosis with or without pustulotic arthro-osteitis (PAO) for no less than 24 weeks PPPASI total score of ≥12 at screening and at baseline Moderate or severe pustules/vesicles on palms or soles (PPPASI severity score ≥2) at screening and at baseline Inadequate response (defined as repeated relapsing-remitting in the same location for a 24-week period) to topical treatments prior to or at screening Key Exclusion Criteria Changes in disease severity during screening (PPPASI total score change ≥ 5 improvement, from screening to baseline) Periodontitis requiring treatment Chronic or recurrent tonsillitis or sinusitis requiring any continuous treatment Has a diagnosis of plaque-type psoriasis at baseline Has the presence of pustular psoriasis on any part of the body other than the palms and soles Has evidence of skin conditions of hand and feet at baseline that would interfere with evaluations of the effect of Investigational Product Has unstable cardiovascular disease, defined as a recent clinical deterioration or a cardiac hospitalization within 12 weeks prior to screening Malignancy or history of malignancy Participant has received any procedures for focal infection within 24 weeks of baseline Female participants who are breastfeeding or who plan to breastfeed while on study Female participants of childbearing potential with a positive pregnancy test Had prior treatment with apremilast Has a prior medical history of suicide attempt at any time in the participant's lifetime prior to signing of informed consent or randomization, or major psychiatric illness requiring hospitalization within the last 3 years prior to signing of informed consent