Structured illumination microscope apparatus and an image forming apparatus

A structured illumination microscope system comprising:

• a beam splitter that splits a beam from a light source into a plurality of beams;
• a beam selector that selects a first plurality of beams or a second plurality of beams from the plurality of beams;
• a first quarter wave plate configured to be rotatable;
• a second quarter wave plate disposed between the light source and the first quarter wave plate;
• and
• an objective lens, wherein
• an interference fringe pattern is formed on a sample,
• a fast axis of the first quarter wave plate is rotated to be set at a first position when the first plurality of beams are selected,
• the fast axis of the first quarter wave plate is rotated to be set at a second position that is different from the first position when the second plurality of beams are selected, and
• the relationship of 0.20ϕ1×sin (6θ1)≤ϕ2≤0.30ϕ1×sin (6θ1) is established, where θ1 is a first structured illumination direction, ϕ1 is a difference of a phase difference generated by the second quarter wave plate from 90° (quarter wave), and ϕ2 is a difference of a phase difference generated by the first quarter wave plate from 90° (quarter wave).