A data slice control device comprises a monotone increase detection circuit for detecting a monotone increase point of a data signal, a monotone decrease detection circuit for detecting a monotone decrease point of the data signal, a counter for calculating a monotone increase interval value from the monotone increase point to a next monotone increase point, a data holding circuit for calculating a monotone increase monotone decrease interval value from the monotone increase point to the monotone decrease point, a CRI period determination circuit for determining whether the data signal is within a CRI period or not on the basis of the monotone increase interval value and the monotone increase monotone decrease interval value, and a slice level calculation circuit for calculating a slice level from a maximum value and a minimum value of amplitude values of the data signal only when the data signal is within the CRI period.