To improve the safety of a patient retaining device for radiotherapy eliminating a possibility of the collision of a head part retaining device with the head part of the patient in lowering.

This patient retaining device 22 is provided with a seat part 5, a backrest 7 and the head part retaining device 8. A moving device having a Z-axis lifting mechanism 15 and a handle 27 is provided. The Z-axis lifting mechanism 15 vertically moves the seat part 5, while the moving device vertically moves the head part retaining device 8. A gas spring supporting the head part retaining device is installed in the backrest 6. The operation of a reactive force generated by the gas spring caused by the weight of the head part retaining device 8 can reduce a load applied to the handle 27 and rotate the handle 27 at a small force when vertically moving the head part retaining device 8. This constitution can, when a patient sits on the seat part 5, facilitate the adjustment of the speed when lowering the head part retaining device 8, so as to eliminate a danger of the collision of the head part retaining device 8 with the head part 8.