Using scanning gate microscopy (SGM), we study local transport property of molybdenum disulfide (MoS2) transistors. The transistors were fabricated using domain-free monolayer-MoS2 crystals grown by chemical vapor deposition (CVD). We observed two different types of SGM responses in different transistors. One is observed along the contact edge and the other is observed within MoS2 channel. The former one is described as visualization of an injection barrier formed by ohmic contact. On the other hand, the latter one implies that there is a barrier at a boundary of two regions having a different electrical property. We will discuss these results including electron force microscopy and photoluminescence mapping in the presentation.