A blast treatment method for blasting a treatment subject having a bursting charge and a shell for housing therein the bursting charge, the method comprising: an inside explosive disposing step of disposing around the treatment subject an inside explosive to be used to initiate detonation of the bursting charge and to blast the treatment subject; an outside explosive disposing step of disposing at positions on an outer side of the inside explosive an outside explosive having a greater detonation velocity than the inside explosive and used to initiate detonation of the inside explosive; and a blast step of blasting the treatment subject, characterized in that in the blast step, detonation of the outside explosive is simultaneously initiated at a plurality of positions spaced from each other at predetermined intervals along a longitudinal direction of the treatment subject to thereby simultaneously initiate detonation of the inside explosive at a plurality of positions along the longitudinal direction of the treatment subject by the detonation of the outside explosive so that detonation of the bursting charge is initiated by the detonations of the inside explosive, and thereby blasting the treatment subject in such a manner that the detonations of the inside explosive along the longitudinal direction of the treatment subject are completed before the detonation of the bursting charge initiated by the detonations of the inside explosive along the longitudinal direction of the treatment subject is completed. the method comprising: an inside explosive disposing step of disposing around the treatment subject an inside explosive to be used to initiate detonation of the bursting charge and to blast the treatment subject; an outside explosive disposing step of disposing at positions on an outer side of the inside explosive an outside explosive having a greater detonation velocity than the inside explosive and used to initiate detonation of the inside explosive; and a blast step of blasting the treatment subject, characterized in that in the blast step, detonation of the outside explosive is simultaneously initiated at a plurality of positions spaced from each other at predetermined intervals along a longitudinal direction of the treatment subject to thereby simultaneously initiate detonation of the inside explosive at a plurality of positions along the longitudinal direction of the treatment subject by the detonation of the outside explosive so that detonation of the bursting charge is initiated by the detonations of the inside explosive, and thereby blasting the treatment subject in such a manner that the detonations of the inside explosive along the longitudinal direction of the treatment subject are completed before the detonation of the bursting charge initiated by the detonations of the inside explosive along the longitudinal direction of the treatment subject is completed. an inside explosive disposing step of disposing around the treatment subject an inside explosive to be used to initiate detonation of the bursting charge and to blast the treatment subject; an outside explosive disposing step of disposing at positions on an outer side of the inside explosive an outside explosive having a greater detonation velocity than the inside explosive and used to initiate detonation of the inside explosive; and a blast step of blasting the treatment subject, characterized in that in the blast step, detonation of the outside explosive is simultaneously initiated at a plurality of positions spaced from each other at predetermined intervals along a longitudinal direction of the treatment subject to thereby simultaneously initiate detonation of the inside explosive at a plurality of positions along the longitudinal direction of the treatment subject by the detonation of the outside explosive so that detonation of the bursting charge is initiated by the detonations of the inside explosive, and thereby blasting the treatment subject in such a manner that the detonations of the inside explosive along the longitudinal direction of the treatment subject are completed before the detonation of the bursting charge initiated by the detonations of the inside explosive along the longitudinal direction of the treatment subject is completed.