Provided are an ultrasonic cutting element and an ultrasonic treatment tool that are small enough to be used in a flexible endoscope and that can achieve a sufficiently high vibration speed. An ultrasonic cutting element (1) that comprises: a vibrator (30) that has a thin-plate-shaped main body (10), a blade part (15) that is fixed to one end of the main body (10), and a drive part (20) that is provided upon at least one main surface (11) of the main body (10); and a holding member (40) that holds the vibrator (30) at one part of the main body (10). The drive part (20) comprises a piezoelectric actuator that is formed by layering, in order from the main surface (11) side of the main body (10), a lower electrode (22), a piezoelectric film (23), and an upper electrode (24). The vibrator (30) is driven by the drive part (20) and is a flexural vibrator that undergoes both-end free bending vibration in a main surface direction. The holding member (40) supports the vibrator (30) only in a node position for a resonance mode that is for both-end free bending vibration.