The present invention provides a particle therapy system including an irradiation compensating device made up of an energy absorber, a first collimator, and a second collimator for use in a short-range region. The irradiation compensating device is characterized by a mechanism for attaching and detaching the first energy absorber, first collimator, and second collimator. The first collimator is located upstream where the beam diameter is small with a view to suppressing the width of the compensating device, thereby contributing to making the compensating device small and lightweight. The second collimator is located downstream to improve penumbrae.
