To provide comfortable air conditioning for residents by varying the switchingover conditions between cooling mode and air supply mode based on the number of switching times.

An outer air intake damper 2 varies the volume of outer air being taken into an air conditioner body 1. A cooling means, i.e., a cooling coil 5, cools or dehumidifies mixture gas of the outer air and the return air. A thermometer 11 measures outer air temperature, a hygrometer 12 measures humidity of outer air, a thermometer 13 measures indoor temperature and a hygrometer 14 measures indoor humidity. A control means 100 controls a two- way valve 6 based on a signal from the thermometer 13 and also controls the outer air intake damper 2, and the like, while interlocking a fan 8 and a return air fan 9. A count means 15 switches the cooling mode and an outer air introduction value set means 16 varies predetermined outer air introduction conditions based on a count. A memory means 17 stores the outer air introduction conditions, i.e., upper and lower limits of outer air temperature and humidity.