  An equation describing subdiffusion with possible immobilization of particles
is derived by means of the continuous time random walk model. The equation
contains a fractional time derivative of Riemann--Liouville type which is a
differential-integral operator with the kernel defined by the Laplace
transform. We propose the method for calculating the inverse Laplace transform
providing the kernel in the time domain. In the long time limit the
subdiffusion--immobilization process reaches a stationary state in which the
probability density of a particle distribution is an exponential function.
