Cockroaches

i just moved to a new apartment around 4 months ago. it was find until recently i found a big black cockroach running around my house.. luckily my friend killed it. 1 week later the small things keep showing up until now.. i've been killing those small black creature by using the spray that i bought from supermarket and i also use that house thingy but dont have any courage to check it its work or not

my question is how do i prevent those thing to keep showing up in my apartment? i always have a nightmare after killing it

Not to give you more nightmares but have you heard the saying "for every one you see there's 100 more in the walls"?

The point is that even though you killed one, there are at least a few more hiding away. Unfortunately, cockroaches are just a fact of life around most of Japan. The conditions are just to perfect for them. What you can do to help mitigate their appearance is first make sure your apartment is clean, like super clean. Promptly wash dishes, put away food, and wipe down surfaces. Set traps, place bait, and hopefully that should keep them in check. If you're finding it particularly bad and live in an apartment you might need to contact the landlord as they could be coming from another part of the building. In this case you might find them much harder to get rid of.

My suggestion is that, in addition to keeping the house clean, buy those Combat cockroach baits which work really well. I find they work MUCH better than those house traps.

Put the baits behind your refrigerator, as cockroaches love the warmth of the fridge and they breed there. Make sure your balcony doors or windows are closed on dusk, as these pest fly in, in the dark. Your landlord should get the place fumigated if they keep appearing, you will need regular fumigation until there are no more appearing. Their breeding cycle is very short, so you usually cannot kill them in one fumigation. Make sure they are not coming through a small hole under the sink as they are known to live on the drainpipes between apartment floors. You can get rid of them but you must be diligent.

Shift to a new house or upper floor apartment(11th or higher).
Old house or lower floor, you will see them.

i did placing those baits but it still keeps coming up like 7-8 small roaches per day. my landlord did the fumigation already but i think it does not affect that much. is it possible if i just call one by myself?

As I said earlier, one fumigation doesn't eradicate them. You must fumigate every 10 -14 days until there are no more appearing or what are there are dead. It sounds like they are coming from somewhere else internally. I'm sure you can get a Pest Control company to come to your apartment, you may have to pay or get some understanding from your landlord about payment or reimbursement. You may have to move out while they spray. I'm inclined to agree with tokyofriend48, unless you are locked into a contract that cannot be broken, maybe look for a brand new property. Good Luck.