A lawn mower blade mounting structure (20 80 90 100 120 130) includes: a drive hub (26) mounted on an output shaft (16) of a power source (15) and protruding outward beyond the output shaft a friction member (27) for transmitting driving force from the drive hub to a blade holder (28), the drive hub and the friction member having curved surfaces (36, 38) slidable on each other when the drive hub and the friction member are in abutting engagement a grass cutting blade (31) attached to the blade holder and an energy absorbing member (32 82 92 102 122 132) disposed in a space (57) defined by the blade holder and peripheral members, the energy absorbing member being constructed to maintain its shape during normal operating condition but deform when a load exceeding a predetermined value acts on the energy absorbing member.
