A grass-mower, comprising: a collector (700) which possesses a collector main-body (710) which accommodates mowed grass to an inner part; and a collector-door lock mechanism (1000) which performs a lock of a collector-door (711) of the collector main-body (710), characterized in that the grass-mower comprises a manual collector-door lock releasing mechanism (3000) which releases the lock of the collector-door (711) based on a manual operation which is performed in the inner part of the collector main-body (710).