PURPOSE: To enable the determination of the alignment of bases of DNA in a short time with high reliability, by detecting radiations emitted from a plurality of DNA samples which migrate parallel in the vertical direction on a migration plate, and by converting same into the alignment of four kinds of bases of DNA.

CONSTITUTION: Radiations emitted by DNA samples (a) ionize a filler gas such as argon, and make electrons radiate therefrom. These electrons are gathered on an anode wire 4, and a pulse of a current is thereby generated at a position (b) thereon. This pulse is propagated to a position (c) on a delay line and taken outside as signals 12 and 13. The signal 12 taken out is shaped and inputted to a start input terminal 17 of TAC 16, while the signal 13 is shaped and inputted to a stop input terminal 21 of TAC16 after a prescribed time T passes. An output 24 from TAC16 is passed through MCA22, and informations on all channels of MCA22 are transferred to a microcomputer C and then stored in an outside memory 23. When the informations are determined as sufficient for deciding the kinds of bases, the kinds of the bases are decided on the basis of these informations and are stored in a prescribed area of the outside memory.