Found in most gyms, the roman chair is a great piece of equipment for training the hip flexors and abdominals. Like the free hanging version of the leg raise, the first half of the movement, where the athlete brings their legs up to parallel, is dominated by the hip flexor muscles. As the thighs travel past parallel, and the pelvic flexes towards the ribcage, the abdominals are strongly active.
Many people mistake the fatigue of the hip flexors as that of the lower abdominal muscles, hence why it is widely stated that the roman chair leg raise is a lower abdominal exercise, and wrongly advised to only take the thighs up to parallel with the ground.
The exercise can be made harder by keeping the legs extended throughout the leg raise.