The present invention is relative with an information processing method for carrying out processing unit data in which one contents are handled as a data unit. When contents data are to be reproduced/output in succession, the tamper check processing for the next contents data, reproduced next to current contents data, being reproduced, is commenced at timing following the end of the processing of decryption and/or demodulation for the current contents data. This eliminates the time interval during which the processing of decryption/demodulation for the current contents data and the tamper check processing for the next contents data are carried out simultaneously in parallel to prevent the processing load caused by concurrent execution of the tamper check processing and the processing of decryption/demodulation from increasing.