Time-of-flight mass spectrometer

A time-of-flight mass spectrometer including an ion ejector for accelerating target ions by imparting a certain amount of energy to the ions, an ion reflector for reflecting ions ejected from the ion ejector and turning the ions around by an effect of an electric field, an ion detector for detecting the ions reflected by and exiting from the ion reflector, and a reflector driver for driving the ion reflector so as to create a reflecting electric field inside the ion reflector, wherein:

• with X denoting a coordinate along a central axis of the ion reflector, the reflector driver applies a voltage to the ion reflector so as to create, inside an inner hollow area of the ion reflector and along the central axis of the ion reflector, a predetermined potential distribution UA(X) in which the potential monotonously changes over the entire ion reflector and therefore an inverse function XA(U) can be uniquely obtained, thus creating an N-th order focusing position at a position with coordinate X0 and potential E0 inside the ion reflector;
• and
• the reflector driver also applies a voltage to the ion reflector within a space having the N-th order focusing position with coordinate X0 as a starting point and extending into a deeper region, so as to superpose, on the predetermined potential XA(U), a predetermined correcting potential XC(U) which can be approximated by a formula proportional to {U(X)−E0}N+3/2 in a vicinity of the coordinate X0 and which is expressed as a smooth function continuing from the coordinate X0 into the deeper region.