A bag opening apparatus and a bag opening method capable of efficiently opening a bag body in a short period of time are provided. A bag opening apparatus (10) includes a gap formation unit (11) which bends at least a front wall portion (102), of the front wall portion and a back wall portion (103) that constitute a mouth portion (101) of a bag body (100), so as to form a gap. When a first press drive member (23) presses a first holding unit (25) against the front wall portion, a contact part (31) of the first holding unit is swung against urging force of an urging part (33) of the first holding unit to bend the front wall portion.