PURPOSE: To display measurement values accurately by adding uniform random numbers to the output counts from a radiation detector, multiplying the sum by a predetermined coefficient, and omitting the fractions of the product to arrange the digit thereby improving the nonlinearity in the differentiation of least significant digit being displayed.

CONSTITUTION: Radiation H is detected by a detector 1 and a signal is delivered to a preamplifier 2. Output signal (a) from the preamplifier 2 is amplified and filtered through a linear amplifier 3 to produce a signal (b). The level of the signal (b) is decided by a signal channel analyzer 4 and a signal (c) having magnitude larger than a predetermined level is outputted. A counter 5 counts the signal (c) a predetermined time and outputs a count N every time when the counting is ended. Uniform random numbers (r) generated from a random number generator 6 is added 7 to the count N and the sum is fed to an operating unit 8 where the sum is multiplied by a coefficient for unit conversion and the digit is arranged by omitting the fractions of the product thus providing a digit to be displayed.