  We obtained mid-infrared 3.6 and 4.5 micron imaging of a z=6.96 Lyman alpha
emitter (LAE) IOK-1 discovered in the Subaru Deep Field, using Spitzer Space
Telescope Infrared Array Camera observations. After removal of a nearby bright
source, we find that IOK-1 is not significantly detected in any of these
infrared bands to m_3.6 ~ 24.00 and m_4.5 ~ 23.54 at 3 sigma. Fitting
population synthesis models to the spectral energy distribution consisting of
the upper limit fluxes of the optical to infrared non-detection images and
fluxes in detection images, we constrain the stellar mass M* of IOK-1. This LAE
could have either a mass as low as M* <~ 2-9 x 10^8 Msun for the young age (<~
10 Myr) and the low dust reddening (A_V ~ 0) or a mass as large as M* <~ 1-4 x
10^{10} Msun for either the old age (> 100 Myr) or the high dust reddening (A_V
~ 1.5). This would be within the range of masses of z ~ 3-6.6 LAEs studied to
date, ~ 10^6-10^{10} Msun. Hence, IOK-1 is not a particularly unique galaxy
with extremely high mass or low mass but is similar to one of the LAEs seen at
the later epochs.
