The invention relates to a particle counter apparatus for counting particles in a fluid flowing in a pipe or a pipeline. The particle counter apparatus comprises a pipe portion through which the fluid flows, where the pipe portion is provided with a fluid sample outlet for withdrawal of a fluid sample. Furthermore the particle counter apparatus also comprises a first fluid transfer body extending from the fluid sample outlet to a particle counter, and a second fluid transfer body extending from the particle counter to a fluid return outlet mounted in the pipe portion downstream of the fluid sample outlet. In the pipe portion there is mounted a propeller unit comprising a propeller and a generator, with the result that particles are distributed uniformly in the fluid before the withdrawal of fluid samples, and electric power is provided for operation of the particle counter apparatus.